Display Panel, Display Device, Display Module, Electronic Device, and Manufacturing Method of Display Panel

ABSTRACT

Display unevenness in a display panel is suppressed. A display panel with a high aperture ratio of a pixel is provided. The display panel includes a first pixel electrode, a second pixel electrode, a third pixel electrode, a first light-emitting layer, a second light-emitting layer, a third light-emitting layer, a first common layer, a second common layer, a common electrode, and an auxiliary wiring. The first common layer is positioned over the first pixel electrode and the second pixel electrode. The first common layer has a portion overlapping with the first light-emitting layer and a portion overlapping with the second light-emitting layer. The second common layer is positioned over the third pixel electrode. The second common layer has a portion overlapping with the third light-emitting layer. The common electrode has a portion overlapping with the first pixel electrode with the first common layer and the first light-emitting layer provided therebetween, a portion overlapping with the second pixel electrode with the first common layer and the second light-emitting layer provided therebetween, a portion overlapping with the third pixel electrode with the second common layer and the third light-emitting layer provided therebetween, and a portion in contact with a top surface of the auxiliary wiring.

This application is a continuation of copending U.S. application Ser.No. 16/766,886, filed on May 26, 2020 which is a 371 of internationalapplication PCT/IB2018/059087 filed on Nov. 19, 2018 which are allincorporated herein by reference.

TECHNICAL FIELD

One embodiment of the present invention relates to a display panel, adisplay device, a display module, an electronic device, and amanufacturing method of a display panel.

Note that one embodiment of the present invention is not limited to theabove technical field. Examples of the technical field of one embodimentof the present invention include a semiconductor device, a displaydevice, a light-emitting device, an electronic device, a lightingdevice, an input/output device (e.g., a touch panel), a method fordriving any of them, and a method for manufacturing any of them.

BACKGROUND ART

In recent years, display panels with high resolution have been demanded.For example, display panels including a large number of pixels, such asfull high definition (1920×1080 pixels), 4K (e.g., 3840×2160 pixels or4096×2160 pixels), and 8K (e.g., 7680×4320 pixels or 8192×4320 pixels)display panels, have been actively developed.

Furthermore, larger display panels have been required. For example, thescreen size of the mainstream home-use television devices has been 50inches or more diagonally. A larger screen size having a larger numberof pixels allows a larger amount of information to be displayed at atime, and a further increase in screen size of digital signage and thelike has been demanded.

Light-emitting elements utilizing electroluminescence (also referred toas EL elements) have features such as ease of thinning and lightening,high-speed response to an input signal, and driving with adirect-current low voltage source; thus, application of the EL elementsto display panels has been proposed. For example, Patent Document 1discloses a flexible light-emitting device including an organic ELelement.

REFERENCE Patent Document [Patent Document 1] Japanese Published PatentApplication No. 2014-197522 DISCLOSURE OF INVENTION

The aperture ratio of pixels in a top-emission display panel can behigher than that of pixels in a bottom-emission display panel because atransistor, a capacitor, a wiring, and the like can be provided so as tooverlap with a light-emitting region of a light-emitting element in thetop-emission display panel. On the other hand, a common electrode of thetop-emission display panel needs to transmit visible light because lightfrom the light-emitting element is extracted through the commonelectrode. The use of a visible-light-transmitting conductive materialcauses a problem of high resistance of the common electrode. When avoltage drop due to the resistance of the common electrode occurs,potential distribution in a display surface becomes nonuniform, andvariation in luminance of light-emitting elements is caused, whichdegrades display quality.

An object of one embodiment of the present invention is to suppressdisplay unevenness or luminance unevenness of a display panel or adisplay device. Another object of one embodiment of the presentinvention is to provide a display panel or display device with highdisplay quality. Another object of one embodiment of the presentinvention is to provide a display panel or display device with a highaperture ratio of a pixel. Another object of one embodiment of thepresent invention is to provide a highly reliable display panel ordisplay device.

Another object of one embodiment of the present invention is to increasethe size of a display device. Another object of one embodiment of thepresent invention is to provide a display device including a largedisplay region in which a seam is less likely to be recognized. Anotherobject of one embodiment of the present invention is to reduce thethickness or weight of a display device. Another object of oneembodiment of the present invention is to provide a display device thatcan display an image along a curved surface. Another object of oneembodiment of the present invention is to provide a highly browsabledisplay device. Another object of one embodiment of the presentinvention is to provide a novel display panel or display device.

Note that the description of these objects does not disturb theexistence of other objects. One embodiment of the present invention doesnot necessarily achieve all the objects. Other objects can be derivedfrom the description of the specification, the drawings, and the claims.

One embodiment of the present invention is a display panel including afirst pixel electrode, a second pixel electrode, a third pixelelectrode, a first light-emitting layer, a second light-emitting layer,a third light-emitting layer, a first common layer, a second commonlayer, a common electrode, and an auxiliary wiring. The firstlight-emitting layer is positioned over the first pixel electrode. Thesecond light-emitting layer is positioned over the second pixelelectrode. The third light-emitting layer is positioned over the thirdpixel electrode. The first light-emitting layer has a function ofemitting light of a color different from a color of light emitted fromthe second light-emitting layer. The first light-emitting layer has afunction of emitting light of a color identical to a color of lightemitted from the third light-emitting layer. The first common layer ispositioned over the first pixel electrode and the second pixelelectrode. The first common layer includes a portion overlapping withthe first light-emitting layer and a portion overlapping with the secondlight-emitting layer. The second common layer is positioned over thethird pixel electrode. The second common layer includes a portionoverlapping with the third light-emitting layer. The common electrodeincludes a portion overlapping with the first pixel electrode with thefirst common layer and the first light-emitting layer providedtherebetween, a portion overlapping with the second pixel electrode withthe first common layer and the second light-emitting layer providedtherebetween, a portion overlapping with the third pixel electrode withthe second common layer and the third light-emitting layer providedtherebetween, and a portion in contact with a top surface of theauxiliary wiring. The first common layer may include a portion incontact with the second common layer. The first common layer may includea portion overlapping with the second common layer.

The first common layer may be positioned between the first pixelelectrode and the first light-emitting layer. The first common layer maybe positioned between the first light-emitting layer and the commonelectrode.

Another embodiment of the present invention is a display panel includinga first pixel electrode, a second pixel electrode, a third pixelelectrode, a first organic compound layer, a second organic compoundlayer, a common electrode, and an auxiliary wiring. The first organiccompound layer is positioned over the first pixel electrode and thesecond pixel electrode. The second organic compound layer is positionedover the third pixel electrode. The first organic compound layer has afunction of emitting light of a color identical to a color of lightemitted from the second organic compound layer. The common electrodeincludes a portion overlapping with the first pixel electrode with thefirst organic compound layer provided therebetween, a portionoverlapping with the second pixel electrode with the first organiccompound layer provided therebetween, a portion overlapping with thethird pixel electrode with the second organic compound layer providedtherebetween, and a portion in contact with a top surface of theauxiliary wiring. The first organic compound layer may include a portionin contact with the second organic compound layer. The first organiccompound layer may include a portion overlapping with the second organiccompound layer.

The first organic compound layer and the second organic compound layermay each include a stack of a plurality of light-emitting layers. Thefirst organic compound layer and the second organic compound layer mayhave a function of emitting white light.

The auxiliary wiring may be positioned over the same plane as the firstpixel electrode.

The display panel having any of the above structures may further includea transistor, and the auxiliary wiring may be positioned over the sameplane as a gate electrode or a source electrode included in thetransistor.

The first pixel electrode, the second pixel electrode, and the thirdpixel electrode may each include a reflective electrode and atransparent electrode over the reflective electrode.

The common electrode may have both a visible-light-transmitting propertyand a visible-light-reflective property.

It is preferable that the auxiliary wiring not overlap with the firstpixel electrode, the second pixel electrode, or the third pixelelectrode.

Another embodiment of the present invention is a display moduleincluding the display panel having any one of the above structures, andat least one of a connector and an integrated circuit.

Another embodiment of the present invention is a display deviceincluding a first display panel and a second display panel. The firstdisplay panel and the second display panel each have any one of theabove structures. The first display panel includes a first displayregion. The second display panel includes a second display region and avisible-light-transmitting region. The second display region is adjacentto the visible-light-transmitting region. The first display regionincludes a portion overlapping with the visible-light-transmittingregion.

Another embodiment of the present invention is a display deviceincluding a flexible display panel, a first impact attenuating layer, asecond impact attenuating layer, a first support, a second support, afirst gear, and a second gear. The display panel is positioned betweenthe first impact attenuating layer and the second impact attenuatinglayer. The first support overlaps with the display panel with the firstimpact attenuating layer provided therebetween, and the second supportoverlaps with the display panel with the first impact attenuating layerprovided therebetween. The first support is connected to the first gear.The second support is connected to the second gear. The first gear andthe second gear are engaged with each other, whereby the movements ofthe first support and the second support are synchronized. The firstimpact attenuating layer includes a region fixed to the first support, aregion fixed to the second support, and a region fixed to neither thefirst support nor the second support. The display device is configuredto change in shape from one of an opened state in which the firstsupport and the second support are positioned substantially on the sameplane and a folded state in which the first support and the secondsupport overlap with each other to the other. In the folded state, thedisplay panel is folded so that a display surface of the display panelis placed inward. It is preferable that the first impact attenuatinglayer and the second impact attenuating layer each contain at least oneof urethane, acrylic, and silicone.

Another embodiment of the present invention is an electronic deviceincluding the display device having any of the above structures, and atleast one of an antenna, a battery (e.g., a secondary battery), ahousing, a camera, a speaker, a microphone, and an operation button.

Another embodiment of the present invention is a method formanufacturing a display panel, including the steps of forming a firstpixel electrode, a second pixel electrode, and a third pixel electrodeover an insulating surface, forming a first common layer over the firstpixel electrode and the second pixel electrode, forming a second commonlayer over the third pixel electrode in a different step from the stepof forming the first common layer, forming a first light-emitting layerover the first pixel electrode and forming a third light-emitting layerover the third pixel electrode using a first mask, forming a secondlight-emitting layer over the second pixel electrode using a second maskin a different step from the step of forming the first light-emittinglayer, and forming a common electrode over the first common layer, thesecond common layer, the first light-emitting layer, the secondlight-emitting layer, and the third light-emitting layer.

In the above manufacturing method, after the first common layer isformed using a third mask, the third mask may be moved parallel to theinsulating surface by one pixel, and then the second common layer may beformed using the third mask. Alternatively, in the above manufacturingmethod, the first common layer may be formed using the third mask, andthe second common layer may be formed using a fourth mask. At this time,an opening pattern of the third mask is shifted from an opening patternof the fourth mask by one pixel.

Another embodiment of the present invention is a method formanufacturing a display panel, including the steps of forming a firstpixel electrode, a second pixel electrode, and a third pixel electrodeover an insulating surface, forming a first organic compound layer overthe first pixel electrode and the second pixel electrode, forming asecond organic compound layer over the third pixel electrode in adifferent step from the step of forming the first organic compoundlayer, and forming a common electrode over the first organic compoundlayer and the second organic compound layer. The first organic compoundlayer has a function of emitting light of a color identical to a colorof light emitted from the second organic compound layer.

In the above manufacturing method, the first organic compound layer maybe formed using a first mask, and after the first organic compound layeris formed, the first mask may be moved parallel to the insulatingsurface by one pixel, and then the second organic compound layer may beformed using the first mask. Alternatively, in the above manufacturingmethod, the first organic compound layer may be formed using a firstmask, and the second organic compound layer may be formed using a secondmask. At this time, an opening pattern of the first mask is shifted froman opening pattern of the second mask by one pixel.

In any of the above manufacturing methods, an auxiliary wiring may beformed in the step of forming the first pixel electrode, the secondpixel electrode, and the third pixel electrode.

One embodiment of the present invention can suppress display unevennessor luminance unevenness of a display panel or a display device. Oneembodiment of the present invention can provide a display panel ordisplay device with high display quality. One embodiment of the presentinvention can provide a display panel or display device with a highaperture ratio of a pixel. One embodiment of the present invention canprovide a highly reliable display panel or display device.

One embodiment of the present invention can increase the size of adisplay device. One embodiment of the present invention can provide adisplay device including a large display region in which a seam is lesslikely to be recognized. One embodiment of the present invention canreduce the thickness or weight of a display device. One embodiment ofthe present invention can provide a display device that can display animage along a curved surface. One embodiment of the present inventioncan provide a highly browsable display device. One embodiment of thepresent invention can provide a novel display panel or display device.

Note that the description of these effects does not disturb theexistence of other effects.

One embodiment of the present invention does not necessarily achieve allthe effects. Other effects can be derived from the description of thespecification, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIG. 1A is a top view illustrating an example of a display panel andFIGS. 1B and 1C are cross-sectional views illustrating an example of adisplay panel;

FIGS. 2A and 2B are top views illustrating examples of a display paneland FIGS. 2C and 2D are cross-sectional views illustrating examples of adisplay panel;

FIGS. 3A to 3E are cross-sectional views illustrating an example of amethod for manufacturing a display panel;

FIGS. 4A to 4C are top views illustrating an example of a method formanufacturing a display panel;

FIGS. 5A to 5D are cross-sectional views illustrating an example of amethod for manufacturing a display panel;

FIGS. 6A to 6C are cross-sectional views illustrating an example of amethod for manufacturing a display panel;

FIGS. 7A and 7C are top views illustrating examples of a display paneland FIG. 7B is a cross-sectional view illustrating an example of adisplay panel;

FIGS. 8A and 8B are top views illustrating examples of a pixel;

FIGS. 9A and 9C are top views illustrating a comparative example of adisplay panel and FIG. 9B is a cross-sectional view illustrating acomparative example of a display panel;

FIG. 10A is a top view illustrating an example of a display panel andFIG. 10B is a cross-sectional view illustrating an example of a displaypanel;

FIG. 11 is a cross-sectional view illustrating an example of a displaypanel;

FIG. 12A is a top view illustrating an example of a display panel andFIGS. 12B and 12C are perspective views illustrating an arrangementexample of a display panel;

FIGS. 13A and 13B are top views illustrating examples of a display paneland FIG. 13C is a cross-sectional view illustrating an example of adisplay panel;

FIG. 14 is a cross-sectional view illustrating an example of a displaydevice;

FIGS. 15A to 15D are top views illustrating an example of a displaypanel;

FIGS. 16A and 16B are cross-sectional views illustrating examples of adisplay panel;

FIG. 17A is a top view illustrating an example of a display panel andFIG. 17B is a cross-sectional view illustrating an example of a displaypanel;

FIGS. 18A, 18B1, 18B2, 18C1, and 18C2 are cross-sectional viewsillustrating examples of a method for manufacturing a display panel;

FIGS. 19A and 19B are cross-sectional views illustrating examples oftransistors;

FIG. 20A is a block diagram illustrating an example of a pixel and FIG.20B illustrates an example of a pixel;

FIGS. 21A and 21B are timing charts showing operation examples of apixel;

FIGS. 22A to 22D illustrate examples of electronic devices;

FIG. 23 is a cross-sectional STEM image of a connection portion;

FIGS. 24A to 24F are cross-sectional views illustrating an example of amethod for manufacturing a display panel;

FIGS. 25A and 25B are cross-sectional STEM images of auxiliary wirings;

FIG. 26A is a cross-sectional view illustrating an example of a displaypanel and FIG. 26B is a top view illustrating an example of a displaypanel;

FIGS. 27A to 27C are cross-sectional STEM images of connection portions;

FIGS. 28A and 28B are perspective views illustrating samples used in apreservation test of a display panel and FIGS. 28C to 28F arephotographs showing the results of a preservation test of a displaypanel;

FIGS. 29A, 29B, 29C1, and 29D are photographs showing an example of amethod for attaching a display panel, FIG. 29C2 is a side viewillustrating an example of a method for attaching a display panel, andFIG. 29E is a photograph of a display panel;

FIG. 30 is a side view illustrating an example of a display device;

FIGS. 31A and 31B are photographs of a display device of Example;

FIG. 32 is a rear view illustrating an example of a display device;

FIGS. 33A and 33C are bottom views illustrating examples of a displaypanel, FIGS. 33B and 33D are top views illustrating examples of adisplay panel, and FIG. 33E is a side view illustrating an example of adisplay device;

FIGS. 34A to 34C are photographs of a display device of Example;

FIG. 35 shows the results of estimation of aperture ratios of pixels;

FIGS. 36A and 36B are perspective views illustrating a display device ofExample; and

FIGS. 37A to 37D are photographs of a display device of Example.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to the drawings.Note that the present invention is not limited to the followingdescription. It will be readily appreciated by those skilled in the artthat modes and details of the present invention can be modified invarious ways without departing from the spirit and scope of the presentinvention. Thus, the present invention should not be construed as beinglimited to the description in the following embodiments.

Note that in structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and a description thereof isnot repeated. The same hatching pattern is applied to portions havingsimilar functions, and the portions are not denoted by specificreference numerals in some cases.

The position, size, range, or the like of each structure illustrated indrawings is not accurately represented in some cases for easyunderstanding. Therefore, the disclosed invention is not necessarilylimited to the position, size, range, or the like disclosed in thedrawings.

Note that the terms “film” and “layer” can be interchanged with eachother depending on the case or circumstances. For example, the term“conductive layer” can be changed into the term “conductive film”. Also,the term “insulating film” can be changed into the term “insulatinglayer”.

Embodiment 1

In this embodiment, display panels and display devices of one embodimentof the present invention are described with reference to FIGS. 1A to 1Cto FIGS. 18A to 18C2.

The display panel in this embodiment has a top-emission structure andincludes a light-emitting element as a display element.

Specifically, the display panel of one embodiment of the presentinvention includes a first pixel electrode, a second pixel electrode, athird pixel electrode, a first light-emitting layer, a secondlight-emitting layer, a third light-emitting layer, a first commonlayer, a second common layer, a common electrode, and an auxiliarywiring. The first light-emitting layer is positioned over the firstpixel electrode. The second light-emitting layer is positioned over thesecond pixel electrode. The third light-emitting layer is positionedover the third pixel electrode. The first light-emitting layer has afunction of emitting light of a color different from that of lightemitted from the second light-emitting layer. The first light-emittinglayer has a function of emitting light of a color identical to that oflight emitted from the third light-emitting layer. The first commonlayer is positioned over the first pixel electrode and the second pixelelectrode. The first common layer has a portion overlapping with thefirst light-emitting layer and a portion overlapping with the secondlight-emitting layer. The second common layer is positioned over thethird pixel electrode. The second common layer has a portion overlappingwith the third light-emitting layer. The common electrode has a portionoverlapping with the first pixel electrode with the first common layerand the first light-emitting layer provided therebetween, a portionoverlapping with the second pixel electrode with the first common layerand the second light-emitting layer provided therebetween, a portionoverlapping with the third pixel electrode with the second common layerand the third light-emitting layer provided therebetween, and a portionin contact with a top surface of the auxiliary wiring.

When the auxiliary wiring is connected to the common electrode of thelight-emitting element, a voltage drop due to the resistance of thecommon electrode can be inhibited, resulting in a display panel withhigh display quality. The common layers of the light-emitting elementare separated into the first common layer and the second common layer,whereby the aperture ratio of the pixel can be increased. Thus, adecrease in aperture ratio of the pixel caused by the auxiliary wiringin the pixel portion of the display panel can be suppressed. As theaperture ratio of the pixel is higher, the luminance of subpixels neededfor obtaining a certain luminance in the display panel becomes lower,which extends the lifetime of the light-emitting element. Furthermore,the display panel can exhibit a high luminance.

[Comparative Example of Display Panel]

A display panel including an auxiliary wiring, which is a comparativeexample, is described with reference to FIGS. 9A to 9C. FIG. 9A shows atop view of a pixel electrode 111 and an auxiliary wiring 120 includedin the display panel. FIG. 9B shows a cross-sectional view taken alongthe dashed-dotted line X-Y in FIG. 9A.

As illustrated in FIG. 9A, the auxiliary wiring 120 of a commonelectrode 113 and the pixel electrode 111 can be provided over the samesurface (an insulating layer 101 in FIG. 9B). As illustrated in FIG. 9B,an opening portion of an insulating layer 104 is provided over theauxiliary wiring 120, and all EL layers 112 are formed separately foreach color, whereby the auxiliary wiring 120 and the common electrode113 can be connected to each other in a connection portion 122.

Here, the case where one pixel 130 is composed of three subpixels ofred, green, and blue (R, G, and B) is described. In the case where allof the EL layers 112 are formed separately for each color, the number ofdeposition steps is extremely large. Thus, even in the case where thelight-emitting layers are formed separately for each color, layers(e.g., a hole-injection layer, a hole-transport layer, anelectron-transport layer, and an electron-injection layer) which caneach have a structure shared by subpixels of three colors are preferablyformed in one step.

FIG. 9C shows an example of a metal mask that can be used to form the ELlayers 112. With the use of a mask 150, layers having a structure sharedby three subpixels (common layer) can be formed in one step, and the ELlayer 112 is not formed in the connection portion 122. However, in thecase of using the mask, evaporation materials are deposited on a regionover which the mask is placed, leading to deformation or displacement ofa pattern. Thus, in order not to form the EL layer 112 in the connectionportion 122, a non-opening portion of the mask 150 is broadly providedbetween the two pixels 130 (see width W1 of a non-opening portion inFIG. 9C), so that the aperture ratio of the mask 150 is decreased.Furthermore, to prevent generation of a warp of the mask, tension of themask needs to be ensured sufficiently. To keep the strength of the mask,there is a problem in that the width of the non-opening portion of themask cannot be shorter than a certain width.

In view of the above, in one embodiment of the present invention, thecommon layers included in the EL layer are formed in two steps. When thecommon layers are formed in two steps, the aperture ratio of the pixelcan be increased as compared with the case where the common layers areformed in one step. Thus, even when the auxiliary wiring is provided inthe pixel portion in the display panel, a decrease in the aperture ratioof the pixel can be suppressed. Note that the common layers can beformed in three or more steps. However, in this case, the number ofdeposition steps is extremely large; thus, the common layers arepreferably formed in two steps. A specific structure of the displaypanel is described below.

[Specific Example 1 of Display Panel]

Display panels each of which includes an auxiliary wiring and is oneembodiment of the present invention are described with reference toFIGS. 1A to 1C to FIGS. 7A to 7C.

FIG. 1A and FIGS. 2A and 2B each show a top view of a common layer 161 aand a common layer 161 b included in a display panel. FIGS. 2A and 2Bshow modification examples of FIG. 1A. FIG. 1B is a cross-sectional viewtaken along the dashed-dotted line A1-A2 in FIG. 1A. FIG. 1C is across-sectional view taken along the dashed-dotted line A11-A12 in FIG.1A. FIG. 2C is a cross-sectional view taken along the dashed-dotted lineA3-A4 in FIG. 2A. FIG. 2D is a cross-sectional view taken along thedashed-dotted line A5-A6 in FIG. 2A.

FIG. 1B is a cross-sectional view showing a red subpixel (R) and a greensubpixel (G) included in a pixel 130 a and a blue subpixel (B) includedin a pixel 130 b which is adjacent to the pixel 130 a as illustrated inFIG. 1A. Furthermore, FIG. 1C is a cross-sectional view including thered subpixel (R) and the green subpixel (G) included in the pixel 130 aand a red subpixel (R) included in a pixel 130 c which is adjacent tothe pixel 130 a.

The display panel illustrated in FIG. 1B includes the pixel electrodes111 and the auxiliary wiring 120 over the insulating layer 101. The endportion of the pixel electrode 111 and the end portion of the auxiliarywiring 120 are covered with the insulating layer 104. An EL layer isprovided over the pixel electrode 111 through an opening in theinsulating layer 104. The common electrode 113 is provided over theauxiliary wiring 120 and the EL layer. The common electrode 113 isshared by subpixels of a plurality of colors and a plurality of pixels.

The EL layer includes the common layers (the common layer 161 and acommon layer 165 in FIG. 1B) which are shared by the subpixels of aplurality of colors and layers provided for each color (light-emittinglayers 163 in FIG. 1B). Note that the common layer 161 a and the commonlayer 161 b are collectively referred to as the common layer 161 in somecases. Similarly, the light-emitting layers included in the subpixelsare collectively referred to as the light-emitting layers 163, and acommon layer 165 a and a common layer 165 b are collectively referred toas the common layer 165 in some cases. Furthermore, in the drawings, thethicknesses of the light-emitting layers are substantially equal to eachother; however, the thickness of the light-emitting layer may differbetween colors.

The common layer included in the EL layer may be positioned between thepixel electrode and the light-emitting layer or between thelight-emitting layer and the common electrode. This embodiment shows anexample in which the light-emitting element includes both the commonlayer 161 positioned between the pixel electrode 111 and thelight-emitting layer 163 and the common layer 165 positioned between thelight-emitting layer 163 and the common electrode 113; however, thelight-emitting element may include only one of the common layer 161 andthe common layer 165.

As illustrated in FIGS. 1A to 1C, a plurality of light-emitting elementsincluded in the same pixel include the same common layer 161 (the commonlayer 161 a or 161 b), and one of the two light-emitting elementsincluded in the adjacent pixels includes the common layer 161 a, and theother includes the common layer 161 b.

The pixel electrode 111 overlaps with the common electrode 113 with theEL layer provided therebetween. When a voltage higher than the thresholdvoltage of the light-emitting element is applied between the pixelelectrode 111 and the common electrode 113, holes are injected to the ELlayer from the anode side and electrons are injected to the EL layerfrom the cathode side. The injected electrons and holes are recombinedin the EL layer and a light-emitting substance contained in the EL layeremits light.

In the connection portion 122, the auxiliary wiring 120 is in contactwith the common electrode 113. That is, the auxiliary wiring 120 iselectrically connected to the common electrode 113. The common electrode113 is electrically connected to the auxiliary wiring 120, so that avoltage drop due to the resistance of the common electrode 113 can beinhibited. Accordingly, luminance unevenness of the display panel can besuppressed and the display quality of the display panel can be improved.Note that the auxiliary wiring 120 does not overlap with the pixelelectrode 111. Furthermore, the auxiliary wiring 120 is electricallyinsulated from the pixel electrode 111.

In each of the pixel 130 a and a pixel 130 d, the red subpixel (R)includes a light-emitting element 110R illustrated in FIG. 1B. Thelight-emitting element 110R includes the pixel electrode 111, the commonlayer 161 a, a light-emitting layer 163R, the common layer 165 a, andthe common electrode 113. In contrast, in each of the pixel 130 b andthe pixel 130 c, a light-emitting element included in the red subpixel(R) includes neither the common layer 161 a nor the common layer 165 a,and includes the common layer 161 b and the common layer 165 b (see FIG.1C).

In each of the pixel 130 a and the pixel 130 d, the green subpixel (G)includes a light-emitting element 110G illustrated in FIG. 1B. Thelight-emitting element 110G includes the pixel electrode 111, the commonlayer 161 a, a light-emitting layer 163G, the common layer 165 a, andthe common electrode 113. In contrast, in each of the pixel 130 b andthe pixel 130 c, a light-emitting element included in the green subpixel(G) includes neither the common layer 161 a nor the common layer 165 a,and includes the common layer 161 b and the common layer 165 b.

In each of the pixel 130 b and the pixel 130 c, the blue subpixel (B)includes a light-emitting element 110B illustrated in FIG. 1B. Thelight-emitting element 110B includes the pixel electrode 111, the commonlayer 161 b, a light-emitting layer 163B, the common layer 165 b, andthe common electrode 113. In contrast, in each of the pixel 130 a andthe pixel 130 d, a light-emitting element included in the blue subpixel(B) includes neither the common layer 161 b nor the common layer 165 b,and includes the common layer 161 a and the common layer 165 a.

In a region 170, the common layer 161 a and the common layer 161 b arein contact with each other. Similarly, in the region 170, the commonlayer 165 a and the common layer 165 b are in contact with each other.In the region 170, the common layer 165 a is over and in contact withthe common layer 161 a. Similarly, in the region 170, the common layer165 b is over and in contact with the common layer 161 b.

As illustrated in FIG. 1A, regions where neither the common layer 161 anor the common layer 161 b is provided are only the connection portion122 and its surroundings. That is, a plurality of regions where thecommon layer 161 is not provided are apart from one another. In the casewhere the common layer 161 is formed in one step with the use of a metalmask, it is difficult to make the plurality of regions where the commonlayer 161 is not provided apart from one another because of thestructure. Thus, the top surface layout of the common layer 161illustrated in FIG. 1A can be regarded as a characteristic layoutobtained by forming the common layer 161 in a plurality of steps, thatis, a characteristic layout of one embodiment of the present invention.

Note that displacement of the mask or the like at the time of filmformation may result in a portion where the common layer 161 a and thecommon layer 161 b overlap with each other and a portion where thecommon layer 161 a and the common layer 161 b are apart from each other,as illustrated in FIGS. 2A to 2D.

FIG. 2A shows an example in which the common layer 161 a included in thepixel 130 a overlaps with the common layer 161 b included in the pixel130 b and the common layer 161 b included in the pixel 130 c and thecommon layer 161 a included in the pixel 130 d are apart from eachother.

In a region 171 in FIG. 2C, the common layer 161 b is positioned overthe common layer 161 a. Similarly, in the region 171, the common layer165 b is positioned over the common layer 165 a.

In a region 172 in FIG. 2D, the common layer 161 a and the common layer161 b are apart from each other. Similarly, in the region 172, thecommon layer 165 a and the common layer 165 b are apart from each other.

In FIG. 2B, each of the common layers 161 a included in the pixel 130 aand the pixel 130 d overlaps with the common layer 161 b included in thepixel 130 b and is apart from the common layer 161 b included in thepixel 130 c.

Also in FIGS. 2A and 2B, neither the common layer 161 a nor the commonlayer 161 b is provided in the connection portion 122 and itssurroundings. That is, a plurality of regions where the common layer 161is not provided are apart from each other. The top surface layout of thecommon layer 161 illustrated in each of FIGS. 2A and 2B can also beregarded as a characteristic layout obtained by forming the common layer161 in a plurality of steps, that is, a characteristic layout of oneembodiment of the present invention.

Note that in FIG. 1B and FIGS. 2C and 2D, the end portion of the commonlayer 161 and the end portion of the common layer 165 are aligned witheach other; however, one embodiment of the present invention is notlimited thereto.

Since the display panel of one embodiment of the present invention has atop-emission structure, the pixel electrode 111 is an electrode throughwhich light is not extracted. The pixel electrode 111 preferablyincludes a visible-light-reflecting conductive film. Furthermore, in thecase where the light-emitting element has a micro optical resonator(microcavity) structure, the pixel electrode 111 is preferably areflective electrode. The reflective electrode has a visible lightreflectance of higher than or equal to 40% and lower than or equal to100%, and preferably higher than or equal to 70% and lower than or equalto 100%.

In the display panel of one embodiment of the present invention, thepixel electrode 111 and the auxiliary wiring 120 can be formed byprocessing the same conductive film. A material used for the pixelelectrode 111 and the auxiliary wiring 120 preferably has a lowerresistivity than a material used for the common electrode 113.

For the visible-light-reflecting conductive film, for example, a metalmaterial such as aluminum, gold, platinum, silver, nickel, tungsten,chromium, molybdenum, iron, cobalt, copper, or palladium or an alloycontaining any of these metal materials can be used. Lanthanum,neodymium, germanium, or the like may be added to the metal material orthe alloy. Moreover, the conductive film can be formed using an alloycontaining aluminum (an aluminum alloy) such as an alloy of aluminum andtitanium, an alloy of aluminum and nickel, an alloy of aluminum andneodymium, or an alloy of aluminum, nickel, and lanthanum (Al—Ni—La), oran alloy containing silver such as an alloy of silver and copper, analloy of silver, palladium, and copper (Ag—Pd—Cu, also referred to asAPC), or an alloy of silver and magnesium. An alloy containing silverand copper is preferable because of its high heat resistance.Furthermore, when a metal film or a metal oxide film is stacked on andin contact with an aluminum alloy film, oxidation of the aluminum alloyfilm can be suppressed. Examples of materials for the metal film or themetal oxide film include titanium and titanium oxide. Alternatively, avisible-light-transmitting conductive film described later and a filmcontaining the metal material or the alloy may be stacked. For example,a stacked film of silver and indium tin oxide (ITO), a stacked film ofan alloy of silver and magnesium and ITO, or the like can be used.

The EL layer includes at least a light-emitting layer. The EL layer mayinclude a plurality of light-emitting layers. In addition to thelight-emitting layer, the EL layer may include a layer containing asubstance with a high hole-injection property, a substance with a highhole-transport property, a hole-blocking material, a substance with ahigh electron-transport property, a substance with a highelectron-injection property, a substance with a bipolar property (asubstance with a high electron- and hole-transport property), or thelike. The EL layer contains one or more kinds of light-emittingsubstances. The light-emitting substance may be an organic compound oran inorganic compound.

The common layer 161 preferably includes a hole-injection layer. Thecommon layer 161 may further include a hole-transport layer. The commonlayer 165 preferably includes an electron-injection layer. The commonlayer 165 may further include an electron-transport layer.

The hole-injection layer injects holes from an anode to the EL layer andcontains a material with a high hole-injection property. As the materialwith a high hole-injection property, a composite material containing ahole-transport material and an acceptor material (electron-acceptingmaterial) is preferably used.

The hole-transport layer transports the holes, which are injected fromthe anode by the hole-injection layer, to the light-emitting layer andcontains a hole-transport material.

The light-emitting layer contains a light-emitting substance. Note thatas the light-emitting substance, a substance whose emission color isblue, violet, bluish violet, green, yellowish green, yellow, orange,red, or the like is appropriately used. When a plurality oflight-emitting layers are formed using different light-emittingsubstances, different emission colors can be exhibited (for example,complementary emission colors are combined to achieve white lightemission). Furthermore, a stacked-layer structure in which onelight-emitting layer contains two or more kinds of light-emittingsubstances may be employed. There is no particular limitation on thelight-emitting substances that can be used for the light-emitting layer,and a light-emitting substance that converts singlet excitation energyinto light emission in the visible light range or a light-emittingsubstance that converts triplet excitation energy into light emission inthe visible light range can be used. As an example of the light-emittingsubstance that converts singlet excitation energy into light emission, asubstance emitting fluorescence (fluorescent material) can be given. Asexamples of a light-emitting substance that converts triplet excitationenergy into light emission, a substance emitting phosphorescence(phosphorescent material) and a thermally activated delayed fluorescent(TADF) material that exhibits thermally activated delayed fluorescencecan be given. It is preferable that a light-emitting substance thatconverts singlet excitation energy into light emission in the visiblelight range be used as the blue-light-emitting substance andlight-emitting substances that convert triplet excitation energy intolight emission in the visible light range be used as the green- andred-light-emitting substances, in which case the spectrum balancebetween R, G, and B is improved. The light-emitting layer may containone or more kinds of compounds (a host material and an assist material)in addition to a light-emitting substance (guest material). As the hostmaterial and the assist material, one or more kinds of substances havinga larger energy gap than the light-emitting substance (the guestmaterial) are used. As the host material and the assist material,compounds which form an exciplex are preferably used in combination. Toform an exciplex efficiently, it is particularly preferable to combine acompound that easily accepts holes (hole-transport material) and acompound that easily accepts electrons (electron-transport material).

The electron-transport layer transports the electrons, which areinjected from the cathode by the electron-injection layer, to thelight-emitting layer and contains an electron-transport material.

The electron-injection layer injects electrons from the cathode to theEL layer and contains a material with a high electron-injectionproperty.

In the case where the light-emitting element has a microcavitystructure, optical adjustment can be performed by the electrode or theEL layer. In the case where the optical adjustment is performed by usingat least one of layers included in the EL layer, the layer may beprovided for each color like the light-emitting layer. For example, thehole-transport layers are formed with different thicknesses for eachcolor, whereby the optical adjustment may be performed.

For the EL layer, either a low-molecular compound or a high-molecularcompound can be used, and an inorganic compound (e.g., a quantum dotmaterial) may also be used. Each of the layers included in the EL layercan be formed by any of the following methods: an evaporation method(including a vacuum evaporation method), a transfer method, a printingmethod, an inkjet method, a coating method, and the like.

The light-emitting element may be a single element including one ELlayer or a tandem element in which a plurality of EL layers are stackedwith a charge generation layer provided therebetween.

In one embodiment of the present invention, a light-emitting elementcontaining an inorganic compound such as a quantum dot may be employed.

The common electrode 113 is an electrode through which light isextracted. The common electrode 113 preferably includes avisible-light-transmitting conductive film. Furthermore, in the casewhere the light-emitting element has a microcavity structure, the commonelectrode 113 preferably has both a visible-light-transmitting propertyand a visible-light-reflective property, and is preferably atransflective electrode. The transflective electrode has a visible lightreflectance of higher than or equal to 20% and lower than or equal to80%, and preferably higher than or equal to 40% and lower than or equalto 70%.

The visible-light-transmitting conductive film can be formed using, forexample, indium oxide, ITO, indium zinc oxide, zinc oxide (ZnO), galliumzinc oxide (Ga—Zn oxide), or aluminum zinc oxide (Al—Zn oxide).Alternatively, a metal material such as gold, silver, platinum,magnesium, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper,palladium, or titanium; an alloy containing any of these metalmaterials; or a nitride of any of these metal materials (e.g., titaniumnitride) can be used when formed thin enough to have alight-transmitting property. Alternatively, a stacked film of any of theabove materials can be used as the conductive film. For example, astacked film of ITO and an alloy of silver and magnesium is preferablyused, in which case conductivity can be increased. Still alternatively,graphene or the like may be used.

Each of the pixel electrode 111 and the common electrode 113 can beformed by an evaporation method or a sputtering method. Alternatively, adischarging method such as an inkjet method, a printing method such as ascreen printing method, or a plating method can be used.

A manufacturing method of the display panel in FIG. 1B is described withreference to FIGS. 3A to 3E to FIGS. 6A to 6C.

Note that thin films (e.g., insulating films, semiconductor films, andconductive films) included in the display panel can be formed by any ofa sputtering method, a chemical vapor deposition (CVD) method, a vacuumevaporation method, a pulsed laser deposition (PLD) method, an atomiclayer deposition (ALD) method, and the like. As the CVD method, aplasma-enhanced chemical vapor deposition (PECVD) method or a thermalCVD method may be used. As the thermal CVD method, for example, a metalorganic chemical vapor deposition (MOCVD) method may be used.

The thin films included in the display panel (e.g., insulating films,semiconductor films, and conductive films) can be formed by a methodsuch as spin coating, dipping, spray coating, ink-jetting, dispensing,screen printing, or offset printing, or with a doctor knife, a slitcoater, a roll coater, a curtain coater, or a knife coater.

When the thin films included in the display panel are processed, alithography method or the like can be used. Alternatively, island-shapedthin films may be formed by a film formation method using a blockingmask. Alternatively, the thin films may be processed by anano-imprinting method, a sandblasting method, a lift-off method, or thelike. Examples of a photolithography method include a method in which aresist mask is formed over a thin film to be processed, the thin film isprocessed by etching or the like, and the resist mask is removed, and amethod in which a photosensitive thin film is formed, and thephotosensitive thin film is exposed to light and developed to beprocessed into a desired shape.

As light for exposure in a lithography method when using light, lightwith an i-line (with a wavelength of 365 nm), light with a g-line (witha wavelength of 436 nm), light with an h-line (with a wavelength of 405nm), or light in which the i-line, the g-line, and the h-line are mixedcan be used. Alternatively, ultraviolet light, KrF laser light, ArFlaser light, or the like can be used. Exposure may be performed byliquid immersion exposure technique. As the light for exposure, extremeultraviolet (EUV) light or X-rays may also be used. Instead of the lightfor exposure, an electron beam can be used. It is preferable to use EUV,X-rays, or an electron beam because extremely minute processing can beperformed. Note that a photomask is not needed when exposure isperformed by scanning of a beam such as an electron beam.

For etching of the thin film, a dry etching method, a wet etchingmethod, a sandblasting method, or the like can be used.

First, a conductive film 131 is formed over the insulating layer 101(FIG. 3A).

Then, the conductive film 131 is processed to form the pixel electrode111 and the auxiliary wiring 120 over the insulating layer 101 (FIG.3B). After that, the insulating layer 104 is formed to cover the endportion of the pixel electrode 111 and the end portion of the auxiliarywiring 120 (FIG. 3C). The insulating layer 104 is provided with anopening so that the top surface of the pixel electrode 111 and the topsurface of the auxiliary wiring 120 are exposed.

Next, the common layer 161 a is formed using a mask 155 (FIG. 3C andFIG. 4A). As illustrated in FIG. 4A, the mask 155 is provided withopenings so that the common layer 161 a is formed in every other pixelin both the column direction and the row direction. When the commonlayer 161 a is formed in the pixel 130 a in FIG. 4A, the common layer161 a is not formed in four pixels adjacent to the pixel 130 a. Forexample, the common layer 161 a is formed in regions corresponding tothe pixel 130 a and the pixel 130 d and is not formed in regionscorresponding to the pixel 130 b, the pixel 130 c, and the connectionportion 122. The mask 155 is preferably a metal mask.

Then, the mask 155 is moved parallel to the insulating layer 101 by onepixel. The mask 155 moves in one direction, which may be the columndirection or the row direction of the pixel arrangement.

Next, with the mask 155, the common layer 161 b is formed (FIG. 3D andFIG. 4B). As illustrated in FIG. 4B, the mask 155 is shifted by onepixel to form the common layer 161 b in the pixel in which the commonlayer 161 a is not formed. For example, the common layer 161 b is formedin regions corresponding to the pixel 130 b and the pixel 130 c and isnot formed in regions corresponding to the pixel 130 a, the pixel 130 d,and the connection portion 122.

Note that the common layer 161 b may be formed using another mask havingan opening pattern shifted from that of the mask 155 by one pixel.

The common layer 161 is formed in two steps, whereby the common layer161 can be formed in all the pixels and can be prevented from beingformed in the connection portion 122, as illustrated in FIG. 4C. Whenthe common layer 161 is formed in two steps, the aperture ratio of thepixel can be large as compared with the case where the common layer 161is formed in one step.

Next, the light-emitting layer 163B, the light-emitting layer 163G, andthe light-emitting layer 163R are formed in the different steps (FIG. 3Eand FIG. 5A). The formation order of the light-emitting layers is notlimited. In the example of FIG. 3E, the light-emitting layer 163B isformed first. When the light-emitting layers are formed sequentiallyfrom a layer of a color with a short wavelength, a display defect causedby unintentional entry of a light-emitting material into a pixel ofanother color is less likely to occur in some cases.

Layers other than the light-emitting layer may be formed separately foreach color. For example, the hole-injection layer may be formed as thecommon layer 161, and then the hole-transport layer and thelight-emitting layer may be formed separately for each color. At thistime, the hole-transport layer and the light-emitting layer aresuccessively formed, which improves the reliability of thelight-emitting element. Specifically, as illustrated in FIG. 6A, ahole-transport layer for blue light 163B_1 is formed and a bluelight-emitting layer 163B_2 is formed, then as illustrated in FIG. 6B, ahole-transport layer for green light 163G_1 is formed and a greenlight-emitting layer 163G_2 is formed, and then, as illustrated in FIG.6C, a hole-transport layer for red light 163R_1 for red light is formedand a red light-emitting layer 163R_2 is formed. Note that thehole-transport layers may each have an optical adjustment function whenthe thickness of the hole-transport layer differs between colors.

Next, the common layer 165 a is formed using the mask 155 (FIG. 5B).Like the common layer 161 a, the common layer 165 a is formed in regionscorresponding to the pixel 130 a and the pixel 130 d and is not formedin regions corresponding to the pixel 130 b, the pixel 130 c, and theconnection portion 122.

Then, the mask 155 is moved parallel to the insulating layer 101 by onepixel.

Next, the common layer 165 b is formed using the mask 155 (FIG. 5C).Like the common layer 161 b, the common layer 165 b is formed in regionscorresponding to the pixel 130 b and the pixel 130 c and is not formedin regions corresponding to the pixel 130 a, the pixel 130 d, and theconnection portion 122.

Note that the common layer 165 b may be formed using another mask havingan opening pattern shifted from that of the mask 155 by one pixel.

Then, the common electrode 113 is formed to cover the auxiliary wiring120, the common layer 165 a, and the common layer 165 b (FIG. 5D). Thus,the auxiliary wiring 120 is connected to the common electrode 113 in theconnection portion 122.

As described above, the light-emitting layers 163 are formed for eachcolor, and also each of the common layer 161 and the common layer 165 isformed in two steps, whereby the aperture ratio of the pixel can beincreased as compared with the case where each of the common layers isformed in one step. Thus, even when the auxiliary wiring 120 is providedin the pixel portion of the display panel, the aperture ratio of thepixel in the display panel can be increased. Therefore, the luminance ofa subpixel needed for obtaining a certain luminance in the display panelcan be lowered, so that the lifetime of the light-emitting element canbe increased. Since the width of the non-opening portion of the mask 155can be sufficiently secured, sufficiently strong tension can be appliedto the mask 155, which can improve the accuracy of the mask 155.

Note that all of the layers in the EL layer may be common layers sharedby subpixels of a plurality of colors. The display panel can employ notonly a separate coloring method but also a color filter method, forexample.

FIG. 7A is a top view of an EL layer 112 a and an EL layer 112 bincluded in the display panel. FIG. 7B is a cross-sectional view takenalong the dashed-dotted line A7-A8 in FIG. 7A.

FIG. 7B is a cross-sectional view including a red subpixel (R) and agreen subpixel (G) included in the pixel 130 a and a blue subpixel (B)included in the pixel 130 b which is adjacent to the pixel 130 a asillustrated in FIG. 7A.

The display panel illustrated in FIG. 7B includes the pixel electrode111 and the auxiliary wiring 120 over the insulating layer 101. The endportion of the pixel electrode 111 and the end portion of the auxiliarywiring 120 are covered with the insulating layer 104. The EL layer 112 aor the EL layer 112 b is provided over the pixel electrode 111 throughan opening in the insulating layer 104. The common electrode 113 isprovided over the auxiliary wiring 120, the EL layer 112 a, and the ELlayer 112 b. In the connection portion 122, the auxiliary wiring 120 isin contact with the common electrode 113. That is, the auxiliary wiring120 is electrically connected to the common electrode 113. The pixelelectrode 111 overlaps with the common electrode 113 with the EL layer112 a or the EL layer 112 b provided therebetween. A coloring layer CFR,a coloring layer CFG, a coloring layer CFB, a light-blocking layer BM,and the like are positioned on one surface side of a counter substrate121. Examples of the counter substrate 121 include a hard substrate, afilm substrate, and a polarizing plate.

In each of the pixels 130 a and 130 d, the red subpixel (R) includes thelight-emitting element 110R illustrated in FIG. 7B. The light-emittingelement 110R includes the pixel electrode 111, the EL layer 112 a, andthe common electrode 113. Light is extracted from the light-emittingelement 110R to the counter substrate 121 side through the coloringlayer CFR. In contrast, in each of the pixels 130 b and 130 c, thelight-emitting element included in the red subpixel (R) does not includethe EL layer 112 a but includes the EL layer 112 b.

In each of the pixels 130 a and 130 d, the green subpixel (G) includesthe light-emitting element 110G illustrated in FIG. 7B. Thelight-emitting element 110G includes the pixel electrode 111, the ELlayer 112 a, and the common electrode 113. Light is extracted from thelight-emitting element 110G to the counter substrate 121 side throughthe coloring layer CFG. In contrast, in each of the pixels 130 b and 130c, the light-emitting element included in the green subpixel (G) doesnot include the EL layer 112 a but includes the EL layer 112 b.

In each of the pixels 130 b and 130 c, the blue subpixel (B) includesthe light-emitting element 110B illustrated in FIG. 7B. Thelight-emitting element 110B includes the pixel electrode 111, the ELlayer 112 b, and the common electrode 113. Light is extracted from thelight-emitting element 110B to the counter substrate 121 side throughthe coloring layer CFB. In contrast, in each of the pixels 130 a and 130d, the light-emitting element included in the blue subpixel (B) does notinclude the EL layer 112 b but includes the EL layer 112 a.

The light-emitting element included in the subpixel of each colorpreferably emits white light.

In the region 170, the EL layer 112 a is in contact with the EL layer112 b. As in the structures in FIGS. 2A to 2D, displacement of the maskor the like at the time of film formation may result in a portion wherethe EL layer 112 a and the EL layer 112 b overlap with each other and aportion where the EL layer 112 a and the EL layer 112 b are apart fromeach other.

Furthermore, depending on the size of the opening in the mask 155, thecommon layer 161 a and the common layer 161 b are not in contact witheach other in some cases. Even in such a case, whether the common layer161 is formed in one step or in a plurality of steps can be determinedin some cases. For example, some misalignment may occur between thecommon layer 161 a formed in the first step and the common layer 161 bformed in the second step. Thus, as illustrated in FIG. 7C, a distanceWa between the common layer 161 a included in the pixel 130 a and thecommon layer 161 b included in the pixel 130 b may be different from adistance Wb between the common layer 161 a included in the pixel 130 dand the common layer 161 b included in the pixel 130 c. When the commonlayers 161 are formed in two steps, the characteristic layout in whichthe pitch of the common layer 161 differs between columns or rows may beobtained. As described above, the pitches of the common layers 161 aredifferent from each other, and thus it can be confirmed that the commonlayers 161 are formed in a plurality of steps.

Note that in the case where the EL layer includes a layer having highconductivity, current leaks to an adjacent light-emitting elementthrough the layer having high conductivity, so that the light-emittingelement other than a desired light-emitting element might emit light(this phenomenon is also referred to as crosstalk). Since the commonlayers 161 in FIG. 7C are separately provided for each pixel, crosstalkcan be suppressed.

Although the alignment of the subpixels are not limited to the structurein FIG. 1A, the structure in FIG. 1A is preferable because the apertureratio can be increased. FIGS. 8A and 8B illustrate alignment ofsubpixels which are different from that in FIG. 1A. FIG. 8A illustratesan example of stripe arrangement, and FIG. 8B illustrates an example ofmatrix arrangement. In addition to the above, S stripe arrangement,pentile arrangement, Bayer arrangement, or the like can be employed.

The coloring layer is a colored layer that transmits light in a specificwavelength range. For example, a color filter for transmitting light ina red, green, blue, or yellow wavelength range can be used. Examples ofa material that can be used for the coloring layer include a metalmaterial, a resin material, and a resin material containing a pigment ordye.

The light-blocking layer BM is provided between the adjacent coloringlayers. The light-blocking layer BM blocks light emitted from anadjacent light-emitting element to inhibit color mixture between theadjacent light-emitting elements. Here, the coloring layer is providedsuch that its end portion overlaps with the light-blocking layer BM,whereby light leakage can be reduced. For the light-blocking layer BM, amaterial that can block light from the light-emitting element can beused; for example, a black matrix can be formed using a metal materialor a resin material containing a pigment or dye. Note that it ispreferable to provide the light-blocking layer BM in a region other thana pixel portion, such as a driver circuit, in which case undesiredleakage of guided light or the like can be suppressed.

[Specific Example 2 of Display Panel]

FIG. 10A is a top view of a display panel 10A. FIG. 10B is across-sectional view of the display panel 10A. FIG. 10B corresponds to across-sectional view taken along the dashed-dotted line B1-B2 in FIG.10A.

The display panel 10A illustrated in FIG. 10A includes a pixel portion71 and a driver circuit 78. An FPC 74 is connected to the display panel.A connector such as a flexible printed circuit (FPC) or an integratedcircuit (IC) can be connected to the display panel. For example, adisplay module can be fabricated by incorporating a scan line drivercircuit into a display panel and providing a signal line driver circuitexternally.

The display panel 10A is a top-emission display panel employing aseparate coloring method. Since the display panel 10A includes anauxiliary wiring, a voltage drop due to the resistance of the commonelectrode 113 can be suppressed and display unevenness can be reduced.Since the common layers included in the EL layer is formed in two steps,the display panel 10A has a high aperture ratio of a pixel even when thepixel portion 71 includes an auxiliary wiring.

As illustrated in FIG. 10B, the display panel 10A includes a substrate361, an insulating layer 367, transistors 301 and 303, a conductivelayer 307, an insulating layer 314, light-emitting elements 20A, 20B,and 21A, the insulating layer 104, a protective layer 109, auxiliarywirings 120 a and 120 b, a bonding layer 318, a substrate 371, and thelike.

The light-emitting elements 20A, 20B, and 21A each include pixelelectrodes 111 a and 111 b, an EL layer, and the common electrode 113.

The pixel electrode 111 a is electrically connected to the source or thedrain of the transistor 303. They are directly connected to each otheror connected via another conductive layer.

The pixel electrode 111 b included in each of the light-emittingelements 20A, 20B, and 21A functions as an optical adjustment layer.With the light-emitting element having a microcavity structure, lightwith high color purity can be extracted from the display panel. Thestructure of the pixel electrode is not limited to a stacked-layerstructure and may be a single-layer structure.

The insulating layer 104 covers end portions of the pixel electrodes 111a and 111 b. The two adjacent pixel electrodes are electricallyinsulated from each other by the insulating layer 104. The pixelelectrode is also electrically isolated from the auxiliary wiring by theinsulating layer 104.

The EL layer includes the common layer (the common layer 161 and thecommon layer 165 in FIG. 10B) which is shared by the subpixels of aplurality of colors and layers provided for each color (thelight-emitting layers 163 in FIG. 10B). Here, the light-emitting element20A illustrated in FIG. 10B is included in a pixel which also includesthe light-emitting element 20B and is different from a pixel includingthe light-emitting element 21A. The pixel including the light-emittingelement 21A is adjacent to the pixel including the light-emittingelement 20A. The light-emitting elements 20A and 20B included in thesame pixel each include the common layer 161 a and the common layer 165a. The light-emitting element 21A included in the pixel adjacent to thepixel including these two light-emitting elements includes the commonlayer 161 b and the common layer 165 b. In the region 172, the commonlayer 161 a and the common layer 161 b are apart from each other, andsimilarly, the common layer 165 a and the common layer 165 b are apartfrom each other. The light-emitting elements 20A and 21A each include alight-emitting layer 163A, and the light-emitting element 20B includesthe light-emitting layer 163B. That is, here, an example in which thesubpixel including the light-emitting element 20A has the same color asthe subpixel including the light-emitting element 21A and has adifferent color from that of the subpixel including the light-emittingelement 20B is shown. An end portion of the EL layer is covered with thecommon electrode 113. The common electrode 113 covers the end portion ofthe EL layer and is in contact with the insulating layer 104 more on theoutside than the end portion of the EL layer. Further, the commonelectrode 113 is in contact with the auxiliary wiring 120 b in theconnection portion 122.

The protective layer 109 covers an end portion of the common electrode113 and is in contact with the insulating layer 104 more on the outsidethan the end portion of the common electrode 113. Moreover, theprotective layer 109 covers an end portion of the insulating layer 314and an end portion of the insulating layer 104 at and in the vicinity ofan end portion of the display panel 10A and is in contact with aninsulating layer 313 more on the outside than the end portion of theinsulating layer 314 and the end portion of the insulating layer 104. Inthe display panel of this embodiment, the variety of insulating layersand the protective layer 109 are preferably provided so that an endportion of an inorganic film (or an inorganic insulating film) ispositioned outward from an end portion of an organic film and inorganicfilms (or inorganic insulating films) are stacked in contact with eachother at and in the vicinity of the end portion of the display panel.With such a structure, impurities such as moisture are less likely toenter the display panel from the outside of the display panel, wherebydeterioration of the transistor and the light-emitting element can besuppressed.

The auxiliary wirings 120 a and 120 b are electrically connected to thecommon electrode 113 through the opening in the insulating layer 104.The auxiliary wiring 120 a can be formed using the same material and thesame step as those used for the pixel electrode 111 a. The auxiliarywiring 120 b can be formed using the same material and the same step asthose used for the pixel electrode 111 b.

Note that the auxiliary wiring of the common electrode 113 is notnecessarily formed in the same fabrication step as the pixel electrode.For example, the auxiliary wiring can be formed using the same materialand the same step as those used for the wirings included in the displaypanel, or at least one of the electrodes of the display panel. When theauxiliary wiring is formed in the same layer as another conductive layerincluded in the display panel, the auxiliary wiring can be provided forthe display panel without increasing the number of fabrication steps ofthe display panel. In contrast, the auxiliary wiring is formed in alayer different from another conductive layer included in the displaypanel, whereby the auxiliary wiring can have a large area, so that avoltage drop due to the resistance of the common electrode 113 can beeffectively suppressed.

FIG. 11 illustrates an example in which the auxiliary wiring 120 isformed using the same material and the same step as those used for thesource and the drain of the transistor.

In FIG. 11 , all of the layers included in the EL layer are each acommon layer which is shared by the subpixels of a plurality of colors.The EL layer includes at least a light-emitting layer. Thelight-emitting element 20A is included in a pixel which also includesthe light-emitting element 20B and is different from a pixel includingthe light-emitting element 21A. The pixel including the light-emittingelement 21A is adjacent to the pixel including the light-emittingelement 20A. The light-emitting elements 20A and 20B included in thesame pixel each include the EL layer 112 a. The light-emitting element21A included in the pixel adjacent to the pixel including these twolight-emitting elements includes the EL layer 112 b. In the region 172,the EL layer 112 a and the EL layer 112 b are apart from each other. Anend portion of the EL layer is covered with the common electrode 113.The common electrode 113 covers the end portion of the EL layer and isin contact with the insulating layer 104 more on the outside than theend portion of the EL layer. Further, the common electrode 113 is incontact with the auxiliary wiring 120 in the connection portion 122.Although the EL layer 112 a and the EL layer 112 b have a three-layerstructure in FIG. 11 , there is no limitation on the number of ELlayers. A coloring layer CFA, the coloring layer CFB, the light-blockinglayer BM, and the like are positioned on one surface side of thesubstrate 371. The light-emitting element 20A and the light-emittingelement 21A each overlap with the coloring layer CFA. That is, here, anexample in which the subpixel including the light-emitting element 20Aand the subpixel including the light-emitting element 21A exhibit thesame color is shown. The light-emitting element 20B overlaps with thecoloring layer CFB. That is, here, an example in which the subpixelincluding the light-emitting element 20A and the subpixel including thelight-emitting element 20B exhibit different colors is shown.

For the light-emitting element and the auxiliary wiring, the descriptionin Specific example 1 of display panel can be referred to.

The display panel preferably includes the protective layer 109 coveringthe light-emitting element. When a film with a high barrier property isused for the protective layer 109, entry of impurities such as moistureand oxygen into the light-emitting element can be suppressed. Thus,deterioration of the light-emitting element can be suppressed and thereliability of the display panel can be improved.

Since light from the light-emitting element is extracted to the outsideof the display panel through the protective layer 109, the protectivelayer 109 preferably has a high visible-light-transmitting property.

The protective layer 109 preferably includes an inorganic film (or aninorganic insulating film). When the light-emitting element issurrounded by the inorganic film, entry of impurities such as moistureand oxygen from the outside into the light-emitting element can besuppressed. The reaction between impurities and an organic compound or ametal material contained in the light-emitting element might causedeterioration of the light-emitting element. Therefore, deterioration ofthe light-emitting element is suppressed by employing the structure withwhich impurities are less likely to enter the light-emitting element,whereby the reliability of the light-emitting element can be improved.

The inorganic film (or the inorganic insulating film) preferably hashigh moisture resistance through which water is less likely to bediffused and transmitted. The inorganic film (or the inorganicinsulating film) through which one or both of hydrogen and oxygen areless likely to be diffused and transmitted is further preferable. Thus,the inorganic film (or the inorganic insulating film) can function as abarrier film. Diffusion of impurities from the outside into thelight-emitting element can be effectively suppressed, which enables thefabrication of a highly reliable display panel.

The protective layer 109 preferably includes one or more insulatingfilms. For the protective layer 109, an oxide insulating film, a nitrideinsulating film, an oxynitride insulating film, a nitride oxideinsulating film, or the like can be used. Examples of the oxideinsulating film include a silicon oxide film, an aluminum oxide film, agallium oxide film, a germanium oxide film, an yttrium oxide film, azirconium oxide film, a lanthanum oxide film, a neodymium oxide film, ahafnium oxide film, and a tantalum oxide film. Examples of the nitrideinsulating film include a silicon nitride film and an aluminum nitridefilm. Examples of the oxynitride insulating film include a siliconoxynitride film. Examples of the nitride oxide insulating film include asilicon nitride oxide film.

Note that in this specification and the like, oxynitride refers to amaterial that contains more oxygen than nitrogen, and nitride oxiderefers to a material that contains more nitrogen than oxygen.

In particular, a silicon nitride film, a silicon nitride oxide film, andan aluminum oxide film are suitably used for the protective layer 109because those films each have high moisture resistance.

An inorganic film containing ITO, Ga—Zn oxide, Al—Zn oxide, In—Ga—Znoxide, or the like can be used for the protective layer 109. Theinorganic film preferably has high resistance, specifically, higherresistance than the common electrode 113. The inorganic film may furthercontain nitrogen.

The protective layer 109 can be formed by a CVD method, a sputteringmethod, an ALD method, or the like. The protective layer 109 may have astacked-layer structure including two or more insulating films formed bydifferent deposition methods.

A sputtering method and an ALD method are capable of forming a film at alow temperature. An EL layer included in a light-emitting element haslow heat resistance. Therefore, the protective layer 109 formed afterthe fabrication of the light-emitting element is preferably formed at arelatively low temperature, typically a temperature of lower than orequal to 100° C., and a sputtering method and an ALD method aresuitable.

The thickness of the inorganic film formed by a sputtering method ispreferably greater than or equal to 50 nm and less than or equal to 1000nm, further preferably greater than or equal to 100 nm and less than orequal to 300 nm.

The thickness of the inorganic film formed by an ALD method ispreferably greater than or equal to 1 nm and less than or equal to 100nm, further preferably greater than or equal to 5 nm and less than orequal to 50 nm.

The water vapor transmission rate of the protective layer 109 is lowerthan 1×10⁻² g/(m²·day), preferably lower than or equal to 5×10⁻³g/(m²·day), further preferably lower than or equal to 1×10⁻⁴ g/(m²·day),still further preferably lower than or equal to 1×10⁻⁵ g/(m²·day), yetfurther preferably lower than or equal to 1×10⁻⁶ g/(m²·day). The lowerthe water vapor transmission rate is, the more diffusion of water fromthe outside into the transistor and the light-emitting element can bereduced.

The thickness of the protective layer 109 is greater than or equal to 1nm and less than or equal to 1000 nm, preferably greater than or equalto 50 nm and less than or equal to 500 nm, further preferably greaterthan or equal to 100 nm and less than or equal to 300 nm. The thicknessof the insulating layer is preferably small because the thinner theinsulating layer is, the thinner the whole display panel can be. Thethinner the insulating layer is, the more throughput is improved, sothat the productivity of the display panel can be improved.

Examples of an organic insulating material that can be used for theinsulating layer 104 include an acrylic resin, an epoxy resin, apolyimide resin, a polyamide resin, a polyimide-amide resin, apolysiloxane resin, a benzocyclobutene-based resin, and a phenol resin.Instead of the insulating layer 104, an inorganic insulating layer maybe used. An inorganic insulating film that can be used for theprotective layer 109 can be used for the inorganic insulating layer.

When an inorganic insulating film is used for an insulating layercovering an end portion of the pixel electrode, impurities are lesslikely to enter the light-emitting element as compared with the casewhere an organic insulating film is used; therefore, the reliability ofthe light-emitting element can be improved. When an organic insulatingfilm is used for the insulating layer covering the end portion of thepixel electrode, a short circuit in the light-emitting element can beprevented because the organic insulating film has higher step coverageand is less likely to be influenced by the shape of the pixel electrodethan the inorganic insulating film.

Note that the insulating layer 104 and the protective layer 109 can eachhave a single-layer structure or a stacked-layer structure including oneor both of an inorganic insulating film and an organic insulating film.

The substrate 361 and the substrate 371 are bonded to each other with abonding layer 318. A space 105 formed by the substrates 361 and 371 andthe bonding layer 318 is preferably filled with a resin or an inert gassuch as nitrogen or argon.

For the substrates 361 and 371, a material such as glass, quartz, aresin, a metal, an alloy, or a semiconductor can be used. The substrateon the side from which light from the light-emitting element isextracted is formed using a material which transmits the light. Aflexible substrate is preferably used as each of the substrates 361 and371. Furthermore, a polarizing plate may be used as the substrate 361 orthe substrate 371.

In the case where a circularly polarizing plate overlaps with thedisplay panel, a highly optically isotropic substrate is preferably usedas the substrate included in the display panel. A highly opticallyisotropic substrate has a low birefringence (in other words, a smallamount of birefringence).

The absolute value of a retardation (phase difference) of a highlyoptically isotropic substrate is preferably less than or equal to 30 nm,further preferably less than or equal to 20 nm, still further preferablyless than or equal to 10 nm.

Examples of a highly optically isotropic film include a triacetylcellulose (TAC, also referred to as cellulose triacetate) film, acycloolefin polymer (COP) film, a cycloolefin copolymer (COC) film, andan acrylic film.

When a film is used for the substrate and the film absorbs water, theshape of the display panel might be changed, e.g., creases aregenerated. Thus, for the substrate, a film with a low water absorptionrate is preferably used. For example, the water absorption rate of thefilm is preferably 1% or lower, further preferably 0.1% or lower, stillfurther preferably 0.01% or lower.

For the bonding layer, various curable adhesives such as a photocurableadhesive (e.g., an ultraviolet curable adhesive), a reactive curableadhesive, a thermosetting adhesive, and an anaerobic adhesive can beused. Alternatively, an adhesive sheet or the like may be used.

The driver circuit 78 includes the transistor 301. The pixel portion 71includes the transistor 303.

Each transistor includes a gate, a gate insulating layer 311, asemiconductor layer, a back gate, a source, and a drain. The gate (thelower gate in FIG. 10B and FIG. 11 ) and the semiconductor layer overlapwith each other with the gate insulating layer 311 positionedtherebetween. The back gate (the upper gate in FIG. 10B and FIG. 11 )and the semiconductor layer overlap with each other with an insulatinglayer 312 and the insulating layer 313 positioned therebetween.

The structure in which the semiconductor layer where a channel is formedis provided between two gates is used in each of the transistors 301 and303. It is preferable that the two gates be connected to each other andsupplied with the same signal to operate the transistor. Such atransistor can have higher field-effect mobility and thus have higheron-state current than other transistors. Consequently, a circuit capableof high-speed operation can be obtained.

Furthermore, the area occupied by a circuit portion can be reduced. Theuse of the transistor having high on-state current can reduce signaldelay in wirings and can suppress display unevenness even in a displaypanel or a display device in which the number of wirings is increasedbecause of an increase in size or resolution. Alternatively, bysupplying a potential for controlling the threshold voltage to one ofthe two gates and a potential for driving to the other, the thresholdvoltage of the transistor can be controlled.

The structure of the transistor may be different between the drivercircuit 78 and the pixel portion 71. The driver circuit 78 and the pixelportion 71 may each include a plurality of kinds of transistors.

The transistor, the capacitor, the wiring, and the like are provided tooverlap with a light-emitting region of the light-emitting element,whereby the aperture ratio of the pixel portion 71 can be increased.

A material through which impurities such as water and hydrogen are lesslikely to be diffused is preferably used for at least one of theinsulating layers 312, 313, and 314. Diffusion of impurities from theoutside into the transistor can be effectively suppressed, leading toimproved reliability of the display panel. The insulating layer 314functions as a planarization layer.

The insulating layer 367 functions as a base film. A material throughwhich impurities such as water and hydrogen are less likely to bediffused is preferably used for the insulating layer 367.

A connection portion 306 includes the conductive layer 307. Theconductive layer 307 can be formed using the same material and the samestep as those used for the source and the drain of the transistor. Theconductive layer 307 is electrically connected to an external inputterminal through which a signal or a potential from the outside istransmitted to the driver circuit 78. Here, an example in which the FPC74 is provided as an external input terminal is shown. The FPC 74 andthe conductive layer 307 are electrically connected to each otherthrough a connector 319.

As the connector 319, any of various anisotropic conductive films (ACF),anisotropic conductive pastes (ACP), and the like can be used.

[Specific Example of Display Device]

Next, a display device including a plurality of display panels isdescribed with reference to FIGS. 12A to 12C.

FIG. 12A is a top view of a display panel DP and FIGS. 12B and 12C areperspective views of a display device including four display panels DP.

When a plurality of display panels DP are arranged in one or moredirections (e.g., in one column or in matrix), a display device with alarge display region can be manufactured.

In the case where a large display device is manufactured using aplurality of display panels DP, each of the display panels DP is notrequired to be large. Thus, an apparatus for manufacturing the displaypanel DP is not necessarily large, whereby space-saving can be achieved.In addition, since an apparatus for manufacturing small- and medium-sizedisplay panels can be used, there is no need to use a novelmanufacturing apparatus for increasing the size of the display device,which leads to a reduction in manufacturing cost. In addition, adecrease in yield caused by an increase in the size of the display panelDP can be suppressed.

A display portion including a plurality of display panels DP has alarger display region than a display portion including one display panelDP when the display panels DP have the same size, and has an effect ofdisplaying more information at a time, for example.

Here, the case where the display panel DP has a non-display region thatsurrounds the pixel portion 71 is considered. At this time, for example,if output images of a plurality of display panels DP are used to displayone image, the image appears divided to a user of the display device.

Making the non-display regions of the display panels DP small (using thedisplay panels DP with narrow frames) can inhibit an image displayed onthe display panels DP from appearing divided; however, it is difficultto totally remove the non-display regions of the display panels DP.

A small non-display region of the display panel DP leads to a decreasein the distance between an end portion of the display panel DP and anelement in the display panel DP, in which case the element easilydeteriorates by impurities from the outside of the display panel DP insome cases.

Thus, in one embodiment of the present invention, a plurality of displaypanels DP are arranged to partly overlap with one another. In twodisplay panels DP overlapping with each other, at least the displaypanel DP on the display surface side (upper side) includes avisible-light-transmitting region 72 that is adjacent to the pixelportion 71. In one embodiment of the present invention, the pixelportion 71 of the display panel DP on the lower side and thevisible-light-transmitting region 72 of the display panel DP on theupper side overlap with each other.

Therefore, a non-display region between the pixel portions 71 of theoverlapping two display panels DP can be reduced or even removed. As aresult, a large-sized display device in which a joint portion of thedisplay panels DP is hardly seen by the user can be obtained.

At least part of a non-display region of the display panel DP on theupper side is the visible-light-transmitting region 72, and can overlapwith the pixel portion 71 of the display panel DP on the lower side.Furthermore, at least part of a non-display region of the display panelDP on the lower side can overlap with the pixel portion 71 of thedisplay panel DP on the upper side or a visible-light-blocking region 73thereof. It is not necessary to reduce the areas of these non-displayregions because a reduction in the area of the frame of the displaydevice (a reduction in area except a pixel portion) is not affected bythese regions.

A large non-display region of the display panel DP leads to an increasein the distance between the end portion of the display panel DP and anelement in the display panel DP, in which case the deterioration of theelement due to impurities from the outside of the display panel DP canbe suppressed. For example, in the case where an organic EL element isused as a display element, impurities such as moisture and oxygen areless likely to enter (or less likely to reach) the organic EL elementfrom the outside of the display panel DP as the distance between the endportion of the display panel DP and the organic EL element increases.Since a sufficient area of the non-display region of the display panelDP is secured in the display device of one embodiment of the presentinvention, the highly reliable large display device can be fabricatedeven when the display panel DP including an organic EL element or thelike is used.

As described above, when a plurality of display panels DP are providedin the display device, the plurality of display panels DP are preferablyarranged so that the pixel portions 71 are arranged continuously betweenthe adjacent display panels DP.

The display panel DP illustrated in FIG. 12A includes a pixel portion71, a visible light-transmitting region 72, and a visible light-blockingregion 73. The visible-light-transmitting region 72 and thevisible-light-blocking region 73 are each provided adjacent to the pixelportion 71. FIG. 12A shows an example in which the display panel DP isprovided with the FPC 74.

The pixel portion 71 includes a plurality of pixels. Thevisible-light-transmitting region 72 may include a pair of substratesforming the display panel DP, a sealant for sealing the display elementsandwiched between the pair of substrates, and the like. Here, formembers provided in the visible-light-transmitting region 72,visible-light-transmitting materials are used. In thevisible-light-blocking region 73, for example, a wiring electricallyconnected to the pixel in the pixel portion 71 may be provided.Moreover, one or both of a scan line driver circuit and a signal linedriver circuit may be provided for the visible-light-blocking region 73.Furthermore, a terminal connected to the FPC 74, a wiring connected tothe terminal, and the like may be provided for thevisible-light-blocking region 73.

FIGS. 12B and 12C show an example in which the display panels DPillustrated in FIG. 12A are arranged in a 2×2 matrix (two display panelsDP are arranged in the longitudinal direction and the lateraldirection). FIG. 12B is a perspective view of the display surface sideof the display panel DP, and FIG. 12C is a perspective view of the sideopposite to the display surface side of the display panel DP.

Four display panels DP (display panels DPa, DPb, DPc, and DPd) arearranged so as to have regions overlapping with each other.Specifically, the display panels DPa, DPb, DPc, and DPd are arranged sothat the visible-light-transmitting region 72 of one display panel DPhas a region overlapping with the top surface (the display surface side)of the pixel portion 71 of another display panel DP and thevisible-light-blocking region 73 of one display panel DP does notoverlap with the top surface of the pixel portion 71 of another displaypanel DP. In a portion where the four display panels DP overlap witheach other, the display panels DPb, DPc, and DPd overlap with the topsurface of the display panel DPa, the top surface of the display panelDPb, and the top surface of the display panel DPc, respectively.

The short side of the display panel DPa and the short side of thedisplay panel DPb overlap with each other, and part of a pixel portion71 a and part of a visible-light-transmitting region 72 b overlap witheach other. Furthermore, the long side of the display panel DPa and thelong side of the display panel DPc overlap with each other, and part ofthe pixel portion 71 a and part of a visible-light-transmitting region72 c overlap with each other.

Part of a pixel portion 71 b overlap with part of thevisible-light-transmitting region 72 c and part of avisible-light-transmitting region 72 d. In addition, part of a pixelportion 71 c overlaps with part of the visible-light-transmitting region72 d.

Therefore, a region where the pixel portions 71 a to 71 d are placedalmost seamlessly can be a display region 79 of the display device.

Here, it is preferable that the display panel DP have flexibility. Forexample, the pair of substrates forming the display panel DP preferablyhas flexibility.

Thus, as illustrated in FIGS. 12B and 12C, a region near an FPC 74 a ofthe display panel DPa can be bent so that part of the display panel DPaand part of the FPC 74 a can be placed under the pixel portion 71 b ofthe display panel DPb adjacent to the FPC 74 a. As a result, the FPC 74a can be placed without physical interference with the rear surface ofthe display panel DPb. Furthermore, when the display panel DPa and thedisplay panel DPb overlap with each other and are fixed, it is notnecessary to consider the thickness of the FPC 74 a; thus, the topsurface of the visible-light-transmitting region 72 b and the topsurface of the display panel DPa can be substantially leveled. This canmake an end portion of the display panel DPb over the pixel portion 71 aless noticeable.

Moreover, each display panel DP has flexibility, whereby the displaypanel DPb can be curved gently so that the top surface of the pixelportion 71 b of the display panel DPb and the top surface of the pixelportion 71 a of the display panel DPa are equal to each other in height.Thus, the heights of the display regions can be equal to each otherexcept in the vicinity of the region where the display panel DPa and thedisplay panel DPb overlap with each other, so that the display qualityof a picture displayed on the display region 79 can be improved.

Although the relation between the display panel DPa and the displaypanel DPb is taken as an example in the above description, the same canapply to the relation between any other two adjacent display panels DP.

To reduce the step between two adjacent display panels DP, the thicknessof the display panel DP is preferably small. For example, the thicknessof the display panel DP is preferably less than or equal to 1 mm,further preferably less than or equal to 300 μm, still furtherpreferably less than or equal to 100 μm.

[Specific Example 3 of Display Panel]

FIGS. 13A and 13B are top views of display panels 15A. FIG. 13C is across-sectional view taken along the dashed-dotted line C1-C2 in FIG.13A.

The display panels illustrated in FIGS. 13A and 13B each include thepixel portion 71, the visible-light-transmitting region 72, and thedriver circuit 78. An FPC 74 is connected to the display panel. FIGS.13A and 13B each illustrate an example in which thevisible-light-transmitting region 72 is adjacent to the pixel portion 71and provided along two sides of the pixel portion 71.

The display panel illustrated in FIG. 13A has a sharp corner and thedisplay panel illustrated in FIG. 13B has a rounded corner. A displaypanel using a film substrate can be fabricated to have various topsurface shapes. For example, a display panel with a corner having acurvature is easily fabricated in some cases because the display panelis less likely to be cracked when the display panel is divided.

The display panel 15A is a top-emission display panel employing aseparate coloring method. The display panel 15A includes thevisible-light-transmitting region 72 along two sides. Since the leadwiring of the common electrode 113 cannot be provided in thevisible-light-transmitting region 72, the influence of a voltage dropbecomes more significant. When the display device illustrated in FIGS.12A to 12C is fabricated using a plurality of display panels 15A and avoltage drop occurs, discontinuous luminance between adjacent displaypanels is easily recognized as luminance unevenness of the whole displaydevice. However, since the display panel 15A includes the auxiliarywiring, a voltage drop due to the resistance of the common electrode 113can be suppressed to reduce display unevenness. Since the common layerincluded in the EL layer is formed in two steps, the aperture ratio of apixel in the display panel 15A is high even when the pixel portion 71includes an auxiliary wiring.

As illustrated in FIG. 13C, the display panel 15A includes the substrate361, a bonding layer 363, an insulating layer 365, the transistors 301and 303, the conductive layer 307, the insulating layer 314, thelight-emitting elements 20A, 20B, and 21A, the insulating layer 104, theprotective layer 109, the auxiliary wirings 120 a and 120 b, a bondinglayer 317, the substrate 371, and the like.

The substrate 361 and the substrate 371 are bonded to each other withthe bonding layer 317. The substrate 361 and the insulating layer 365are bonded to each other with the bonding layer 363.

In the fabrication of the display panel 15A, the transistor, thelight-emitting element, and the like formed over a formation substrateare transferred to the substrate 361.

The light-emitting elements 20A, 20B, and 21A each include the pixelelectrodes 111 a and 111 b, an EL layer, and the common electrode 113.

The pixel electrode 111 a is electrically connected to the source or thedrain of the transistor 303. They are directly connected to each otheror connected via another conductive layer.

The pixel electrode 111 b included in each of the light-emittingelements 20A, 20B, and 21A functions as an optical adjustment layer.FIG. 10B and the like each illustrate an example in which the pixelelectrode 111 b covers the pixel electrode 111 a; however, asillustrated in FIG. 13C, the pixel electrode 111 b does not necessarilycover the side surface of the pixel electrode 111 a.

The driver circuit 78 includes the transistor 301. The pixel portion 71includes the transistor 303.

Each transistor includes a back gate, the gate insulating layer 311, asemiconductor layer, a gate insulating layer, a gate, an insulatinglayer 315, a source, and a drain. The semiconductor layer includes achannel formation region and a pair of low-resistance regions. The backgate (the lower gate in FIG. 13C) and the channel formation regionoverlap with each other with the gate insulating layer 311 positionedtherebetween. The gate (the upper gate in FIG. 13C) and the channelformation region overlap with each other with the gate insulating layerpositioned therebetween. The source and the drain are electricallyconnected to the low-resistance regions through openings provided in theinsulating layer 315.

The above description of the display panel 10A (FIG. 10B) can bereferred to for the structures of the pixel portion 71, the drivercircuit 78, and the connection portion 306 of the display panel 15Aillustrated in FIG. 13C because the structures are in common with thosein the display panel 10A in many points.

The layers included in the visible-light-transmitting region 72 transmitvisible light. FIG. 13C illustrates an example in which thevisible-light-transmitting region 72 includes the substrate 361, thebonding layer 363, the insulating layer 365, the gate insulating layer311, the insulating layer 315, the protective layer 109, the bondinglayer 317, and the substrate 371. In this stacked-layer structure, thematerials for the layers are preferably selected such that a differencein refractive index at each interface is minimized. A difference inrefractive index between two layers that are in contact with each otheris reduced, so that a junction between the two display panels cannot beeasily recognized by a user.

It is preferable that the number of insulating layers in thevisible-light-transmitting region 72 be smaller than that in a region ofthe pixel portion 71 in the vicinity of the visible-light-transmittingregion 72. The number of insulating layers included in thevisible-light-transmitting region 72 is reduced, and thus the number ofinterfaces at which a difference in refractive index is large can bereduced. Thus, the reflection of external light in thevisible-light-transmitting region 72 can be suppressed. In this case,the visible light transmittance in the visible-light-transmitting region72 can be increased. Thus, the difference in the luminance (brightness)of display on the display panel on the lower side between a portion seenthrough the visible-light-transmitting region 72 and a portion seen notthrough the region can be small. Accordingly, the display unevenness orluminance unevenness of the display device can be suppressed.

FIG. 14 illustrates an example of a cross-sectional view of a displaydevice in which two display panels 15A illustrated in FIG. 13C overlapwith each other.

In the display device illustrated in FIG. 14 , the display panelpositioned on the display surface side (upper side) includes thevisible-light-transmitting region 72 adjacent to the pixel portion 71.The pixel portion 71 of the lower display panel and thevisible-light-transmitting region 72 of the upper display panel overlapwith each other. The visible-light-blocking region of the lower displaypanel (e.g., the driver circuit 78 and the connection portion 306)overlaps with the pixel portion 71 of the upper display panel.Therefore, a non-display region between the pixel portions of theoverlapping two display panels can be reduced or even removed.Accordingly, a large display device in which a junction between displaypanels is less likely to be noticed by a user can be obtained.

The display device illustrated in FIG. 14 includes a light-transmittinglayer 102 having a refractive index higher than that of air andtransmitting visible light between the pixel portion 71 of the lowerdisplay panel and the visible-light-transmitting region 72 of the upperdisplay panel. Thus, air can be suppressed from entering between the twodisplay panels, so that the interface reflection due to a difference inrefractive index can be reduced. In addition, display unevenness orluminance unevenness of the display device can be suppressed.

Next, a structure of the common layer in a region N in FIG. 13A isdescribed with reference to FIGS. 15A to 15D. Here, the case where thecommon layers 161 a and 161 b are formed using one mask 155 isdescribed.

After the common layer 161 a is formed using the mask 155 as illustratedin FIG. 15A, the mask 155 is shifted in the X direction or the Ydirection by one pixel, whereby the common layer 161 b can also beformed using the same mask 155. FIG. 15B shows the case where the mask155 is shifted in the X direction by one pixel, and the common layer 161b is formed. Here, as illustrated in FIG. 15B, the common layer 161 b isformed also in the visible-light-transmitting region 72 in the Ydirection per pixel. FIG. 15C is a top view of the common layers 161 aand 161 b. In this case, as illustrated in FIG. 15D, it is preferablethat the common electrode 113 cover the common layer 161 b formed in thevisible-light-transmitting region 72 and the end portion of the commonelectrode 113 be positioned outward from the end portion of the commonlayer 161 b. In particular, the end portion of the common electrode 113is preferably in contact with an inorganic film. This can suppress entryof impurities into the common layer 161 b in thevisible-light-transmitting region 72.

Note that the above structure can be used not only in the region N inFIG. 13A but also in the region N in FIG. 10A. In other words, when thecommon layer 161 a and the common layer 161 b are formed using one mask,the common layers 161 a or the common layers 161 b are provided outsidethe pixel portion 71 of the display panel with substantially the samepitches. This can also be a feature obtained by forming the common layer161 in a plurality of steps, that is, a feature of one embodiment of thepresent invention.

Furthermore, FIGS. 16A and 16B show a modification example of thedisplay panel. The display panel illustrated in FIGS. 16A and 16B isformed by transferring a protective layer 375 and the light-blockinglayer BM formed over the formation substrate to the substrate 371. Thesubstrate 371 and the protective layer 375 are bonded to each other witha bonding layer 373. In this manner, the protective layer 109 over thelight-emitting element is not provided, and a protective layer may beprovided on the counter substrate side.

In FIG. 16A, the source or the drain of the transistor 303 iselectrically connected to the pixel electrode 111 a of thelight-emitting element through a conductive layer 128 a. In this manner,the light-emitting element and the transistor may each be provided witha layer of a conductive layer. Specifically, the conductive layer 128 ais provided over the insulating layer 314 a covering the transistor 303,the insulating layer 314 b is provided over the conductive layer 128 a,and the pixel electrode 111 a is provided over the insulating layer 314b. The pixel electrode 111 a is connected to the conductive layer 128 athrough an opening in the insulating layer 314 b, and the conductivelayer 128 a is connected to the source or the drain of the transistor303 through an opening in the insulating layer 314 a. A conductive layer128 b is provided over the insulating layer 314 a. The conductive layer128 b can be formed using the same material and the same step as thoseused for the conductive layer 128 a. Since the conductive layer 128 b iselectrically connected to the common electrode 113, the conductive layer128 b can function as an auxiliary wiring of the common electrode 113.In the connection portion 122, the common electrode 113 is connected tothe auxiliary wiring 120 b through an opening in the insulating layer104. The auxiliary wiring 120 b is provided over and in contact with theauxiliary wiring 120 a. The auxiliary wiring 120 a is connected to theconductive layer 128 b through an opening in the insulating layer 314 b.In this manner, the common electrode 113 may be electrically connectedto both the conductive layer that is in the same layer as the pixelelectrode and the conductive layer that is in another layer. Theauxiliary wirings 120 a and 120 b are not necessarily provided, and thecommon electrode 113 may be directly connected to the conductive layer128 b.

FIG. 16B illustrates an example in which the layer of the auxiliarywiring 120 is provided separately from the layer of the transistor, thewiring, and the light-emitting element. The layer of only the auxiliarywiring 120 is provided, whereby the auxiliary wiring 120 having a largearea can be provided. Accordingly, a voltage drop due to the resistanceof the common electrode 113 can be suppressed more effectively. In FIG.16B, the conductive layer 128 is provided over the insulating layer 314a, the insulating layer 314 b is provided over the conductive layer 128,the auxiliary wiring 120 is provided over the insulating layer 314 b,and an insulating layer 314 c is provided over the auxiliary wiring 120.The common electrode 113 is electrically connected to the auxiliarywiring 120 through an opening provided in the insulating layer 104 andthe insulating layer 314 c. The conductive layer 128 is electricallyconnected to the transistor through an opening provided in theinsulating layer 314 a. The pixel electrode is electrically connected tothe conductive layer 128 through an opening provided in the insulatinglayer 314 b and the insulating layer 314 c.

[Specific Example 4 of Display Panel]

FIG. 17A is a top view of a display panel 15B. FIG. 17B is across-sectional view taken along the dashed-dotted line C3-C4 in FIG.17A.

The display panel 15B illustrated in FIG. 17A includes the pixel portion71, the visible-light-transmitting region 72, and the driver circuit 78.The FPC 74 is connected to the display panel 15B. While the displaypanel 15A (FIG. 13A) has a structure in which the FPC 74 is connected onthe display surface side, the display panel 15B has a structure in whichthe FPC 74 is connected on the side opposite to the display surface (therear surface side). FIG. 17A shows an example in which thevisible-light-transmitting region 72 is adjacent to the pixel portion 71and provided along two sides of the pixel portion 71.

The display panel 15A and the display panel 15B are different from eachother mainly in the structure of the connection portion 306.

In the connection portion 306 of the display panel 15B, a conductivelayer 309 is electrically connected to the FPC 74 through the connector319. The conductive layer 309 is electrically connected to theconductive layer 308 through an opening in the insulating layer 365.

Next, a method for manufacturing the display panel 15B is described witha focus on the connection portion 306 with reference to FIGS. 18A to18C2.

First, a separation layer 353 is formed over a formation substrate 351,and a layer to be separated is formed over the separation layer 353(FIG. 18A). The layer to be separated is formed in the following manner.First, the conductive layer 309 is formed over the separation layer 353,the insulating layer 365 is formed over the separation layer 353 and theconductive layer 309, and an opening overlapping with the conductivelayer 309 is provided in the insulating layer 365. Then, the conductivelayer 308 which is connected to the conductive layer 309 through theopening is formed. The conductive layer 308 can be formed using the samematerial and the same step as those used for the gate of the transistor.Note that the conductive layer 308 may be formed using the same materialand the same step as those used for the source and the drain of thetransistor. Then, the gate insulating layer 311 to the substrate 371 areformed in this order.

Next, the formation substrate 351 is separated. FIG. 18B1 illustrates anexample in which separation occurs at the interface between theseparation layer 353 and the conductive layer 309 and the interfacebetween the separation layer 353 and the insulating layer 365. Thus, theconductive layer 309 can be exposed. Then, as illustrated in FIG. 18C1,the conductive layer 309 can be electrically connected to the FPC 74using the connector 319.

As illustrated in FIG. 18B2, separation might occur in the separationlayer 353. At this time, a separation layer 353 a remains on theformation substrate 351 side and a separation layer 353 b remains incontact with the conductive layer 309. In the case where the conductivelayer 309 is not exposed after the separation of the formation substrate351, the conductive layer 309 is preferably exposed by removing part ofthe separation layer 353 b. Then, as illustrated in FIG. 18C2, theconductive layer 309 can be electrically connected to the FPC 74 usingthe connector 319.

The fabrication substrate 351 has stiffness high enough for easytransfer and has resistance to heat applied in the manufacturingprocess. Examples of a material that can be used for the formationsubstrate 351 include glass, quartz, ceramics, sapphire, a resin, asemiconductor, a metal, and an alloy. Examples of the glass includealkali-free glass, barium borosilicate glass, and aluminoborosilicateglass.

The separation layer 353 can be formed using an organic material or aninorganic material.

Examples of an organic material that can be used for the separationlayer 353 include a polyimide resin, an acrylic resin, an epoxy resin, apolyamide resin, a polyimide-amide resin, a siloxane resin, abenzocyclobutene-based resin, and a phenol resin.

Examples of an inorganic material that can be used for the separationlayer 353 include a metal containing an element selected from tungsten,molybdenum, titanium, tantalum, niobium, nickel, cobalt, zirconium,zinc, ruthenium, rhodium, palladium, osmium, iridium, and silicon; analloy containing any of the above elements; and a compound containingany of the above elements. A crystal structure of a layer containingsilicon may be amorphous, microcrystal, or polycrystal.

The formation substrate 351 may be separated by irradiating theseparation interface with a laser. As the laser, an excimer laser, asolid laser, or the like can be used. For example, a diode-pumpedsolid-state laser (DPSS) may be used. Alternatively, the formationsubstrate 351 may be separated when a perpendicular tensile force isapplied to the separation layer 353.

To the display panel 15B, the FPC 74 is connected to the side oppositeto the display surface (rear surface side). For example, by using thedisplay panel 15B, a multidisplay in FIG. 32 to be described in Example2 can be fabricated.

<Structure Example of Transistor>

Next, transistors that can be used for the display panel or the displaydevice are described.

The structure of the transistors in the display panel or the displaydevice is not particularly limited. For example, a planar transistor, astaggered transistor, or an inverted staggered transistor may be used. Atop-gate transistor or a bottom-gate transistor may be used. Gateelectrodes may be provided above and below a channel.

FIGS. 19A and 19B illustrate structure examples of transistors. Eachtransistor is provided between an insulating layer 141 and an insulatinglayer 208. The insulating layer 141 preferably functions as a base film.The insulating layer 208 preferably functions as a planarization film.

A transistor 220 illustrated in FIG. 19A is a bottom-gate transistorcontaining a metal oxide in a semiconductor layer 204. The metal oxidecan function as an oxide semiconductor.

An oxide semiconductor is preferably used as the semiconductor of thetransistor. The use of a semiconductor material having a wider band gapand a lower carrier density than silicon is preferable because off-statecurrent of the transistor can be reduced.

The transistor 220 includes the conductive layer 201, the insulatinglayer 202, the conductive layer 203 a, the conductive layer 203 b, andthe semiconductor layer 204. The conductive layer 201 functions as agate. The insulating layer 202 functions as a gate insulating layer. Thesemiconductor layer 204 overlaps with the conductive layer 201 with theinsulating layer 202 positioned therebetween. The conductive layers 203a and 203 b are electrically connected to the semiconductor layer 204.The transistor 220 is preferably covered with insulating layers 211 and212. Various inorganic insulating films can be used for the insulatinglayers 211 and 212. In particular, an oxide insulating film is suitablyused for the insulating layer 211, and a nitride insulating film issuitably used for the insulating layer 212.

A transistor 230 illustrated in FIG. 19B is a top-gate transistorcontaining polysilicon in the semiconductor layer.

The transistor 230 includes the conductive layer 201, the insulatinglayer 202, the conductive layer 203 a, the conductive layer 203 b, thesemiconductor layer, and an insulating layer 213. The conductive layer201 functions as a gate. The insulating layer 202 functions as a gateinsulating layer. The semiconductor layer includes a channel formationregion 214 a and a pair of low-resistance regions 214 b. Thesemiconductor layer may further include a lightly doped drain (LDD)region. FIG. 19B illustrates an example in which an LDD region 214 c isprovided between the channel formation region 214 a and thelow-resistance region 214 b. The channel formation region 214 a overlapswith the conductive layer 201 with the insulating layer 202 providedtherebetween. The conductive layer 203 a is electrically connected toone of the pair of low-resistance regions 214 b through an opening inthe insulating layer 202 and the insulating layer 213. Similarly, theconductive layer 203 b is electrically connected to the other of thepair of low-resistance regions 214 b. Various inorganic insulating filmscan be used for the insulating layer 213. In particular, a nitrideinsulating film is suitably used for the insulating layer 213.

[Metal Oxide]

For the semiconductor layer, a metal oxide functioning as an oxidesemiconductor is preferably used. A metal oxide that can be used for thesemiconductor layer is described below.

The metal oxide preferably contains at least indium or zinc. Inparticular, indium and zinc are preferably contained. In addition,aluminum, gallium, yttrium, tin, or the like is preferably contained.Furthermore, one or more elements selected from boron, titanium, iron,nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium,hafnium, tantalum, tungsten, magnesium, and the like may be contained.

Here, the case where the metal oxide is an In-M-Zn oxide that containsindium, an element M, and zinc is considered. The element M is aluminum,gallium, yttrium, tin, or the like. Other elements that can be used asthe element M include boron, titanium, iron, nickel, germanium,zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum,tungsten, and magnesium. Note that two or more of the above elements maybe used in combination as the element M.

Note that in this specification and the like, a metal oxide containingnitrogen is also called a metal oxide in some cases. Moreover, a metaloxide containing nitrogen may be called a metal oxynitride. For example,a metal oxide containing nitrogen, such as zinc oxynitride (ZnON), maybe used for a semiconductor layer.

An oxide semiconductor (metal oxide) is classified into a single crystaloxide semiconductor and a non-single-crystal oxide semiconductor.Examples of the non-single-crystal oxide semiconductor include ac-axis-aligned crystalline oxide semiconductor (CAAC-OS), apolycrystalline oxide semiconductor, a nanocrystalline oxidesemiconductor (nc-OS), an amorphous-like oxide semiconductor (a-likeOS), and an amorphous oxide semiconductor.

The CAAC-OS has c-axis alignment, its nanocrystals are connected in thea-b plane direction, and its crystal structure has distortion. Note thatdistortion refers to a portion where the direction of a latticearrangement changes between a region with a uniform lattice arrangementand another region with a uniform lattice arrangement in a region wherethe nanocrystals are connected.

The shape of the nanocrystal is basically a hexagon but is not always aregular hexagon and is a non-regular hexagon in some cases. A pentagonallattice arrangement, a heptagonal lattice arrangement, or the like isincluded in the distortion in some cases. Note that it is difficult toobserve a clear crystal grain boundary even in the vicinity ofdistortion in the CAAC-OS. That is, a lattice arrangement is distortedand thus formation of a grain boundary is inhibited. This is because theCAAC-OS can tolerate distortion owing to a low density of oxygen atomarrangement in the a-b plane direction, a change in interatomic bonddistance by substitution of a metal element, and the like.

The CAAC-OS tends to have a layered crystal structure (also referred toas a layered structure) in which a layer containing indium and oxygen(hereinafter, In layer) and a layer containing the element M, zinc, andoxygen (hereinafter, (M, Zn) layer) are stacked. Note that indium andthe element M can be replaced with each other, and when the element M ofthe (M, Zn) layer is replaced with indium, the layer can also bereferred to as an (In, M, Zn) layer. When indium of the In layer isreplaced with the element M, the layer can also be referred to as an(In, M) layer.

The CAAC-OS is a metal oxide with high crystallinity. By contrast, inthe CAAC-OS, a reduction in electron mobility due to the crystal grainboundary is less likely to occur because it is difficult to observe aclear crystal grain boundary. Entry of impurities, formation of defects,or the like might decrease the crystallinity of a metal oxide. Thismeans that the CAAC-OS has small amounts of impurities and defects(e.g., oxygen vacancies (Vo)). Thus, a metal oxide including the CAAC-OSis physically stable. Therefore, the metal oxide including the CAAC-OSis resistant to heat and has high reliability.

In the nc-OS, a microscopic region (for example, a region with a sizegreater than or equal to 1 nm and less than or equal to 10 nm, inparticular, a region with a size greater than or equal to 1 nm and lessthan or equal to 3 nm) has a periodic atomic arrangement. There is noregularity of crystal orientation between different nanocrystals in thenc-OS. Thus, the orientation in the whole film is not observed.Accordingly, in some cases, the nc-OS cannot be distinguished from ana-like OS or an amorphous oxide semiconductor, depending on an analysismethod.

Note that indium-gallium-zinc oxide (hereinafter referred to as IGZO)that is a metal oxide containing indium, gallium, and zinc has a stablestructure in some cases by being formed of the above-describednanocrystals. In particular, IGZO crystals tend not to grow in the airand thus, a stable structure is obtained when IGZO is formed of smallercrystals (e.g., the above-described nanocrystals) rather than largercrystals (here, crystals with a size of several millimeters or severalcentimeters).

The a-like OS is a metal oxide having a structure between those of thenc-OS and the amorphous oxide semiconductor. The a-like OS has a void ora low-density region. That is, the a-like OS has low crystallinity ascompared with the nc-OS and the CAAC-OS.

An oxide semiconductor (metal oxide) can have any of various structureswhich show various different properties. Two or more of the amorphousoxide semiconductor, the polycrystalline oxide semiconductor, the a-likeOS, the nc-OS, and the CAAC-OS may be included in an oxide semiconductorof one embodiment of the present invention.

The metal oxide film functioning as a semiconductor layer can be formedusing one or both of an inert gas and an oxygen gas. Note that there isno particular limitation on the flow rate ratio of oxygen (the partialpressure of oxygen) in the step of forming the metal oxide film. In thecase where a transistor having high field-effect mobility is obtained,the flow rate ratio of oxygen (the partial pressure of oxygen) in thestep of forming the metal oxide film is preferably higher than or equalto 0% and lower than or equal to 30%, further preferably higher than orequal to 5% and lower than or equal to 30%, still further preferablyhigher than or equal to 7% and lower than or equal to 15%.

The energy gap of the metal oxide is preferably 2 eV or more, furtherpreferably 2.5 eV or more, still further preferably 3 eV or more. Withthe use of a metal oxide having such a wide energy gap, the off-statecurrent of the transistor can be reduced.

The metal oxide film can be formed by a sputtering method.Alternatively, a PLD method, a PECVD method, a thermal CVD method, anALD method, a vacuum evaporation method, or the like may be used.

As described above, the display panel of this embodiment includes theauxiliary wiring connected to the common electrode of the light-emittingelement and the aperture ratio of the pixel is high. Accordingly,luminance unevenness of the display panel can be suppressed and thedisplay quality of the display panel can be improved. Furthermore, adisplay panel which has high reliability and enables high-luminancedisplay can be obtained.

This embodiment can be combined with any of the other embodiments andthe examples as appropriate. In the case where a plurality of structureexamples are described in one embodiment in this specification, some ofthe structure examples can be combined as appropriate.

Embodiment 2

In this embodiment, a display panel of one embodiment of the presentinvention is described with reference to FIGS. 20A and 20B and FIGS. 21Aand 21B.

FIG. 20A is a block diagram of a pixel. A pixel of this embodimentincludes a memory (Memory) in addition to a switching transistor(Switching Tr), a driving transistor (Driving Tr), and a light-emittingelement (OLED).

Data DATA_W is supplied to the memory. When the data DATA_W is suppliedto the pixel in addition to display data DATA, a current flowing throughthe light-emitting element is large, so that the display panel can havehigh luminance.

10 When the potential of the data DATA_W is represented by V_(w), thepotential of the display data DATA is represented by V_(data), and thecapacitance of the memory is represented by C_(w), the gate voltageV_(g) of the driving transistor can be expressed by Formula (1).

$\left\lbrack {{Formula}1} \right\rbrack\begin{matrix}{V_{g} = {V_{w} + {\frac{C_{w}}{C_{w} + C_{s}}V_{data}}}} & (1)\end{matrix}$

When V_(w) equals to V_(data), a voltage higher than V_(data) is appliedas V_(g), and a larger current can flow. That is, the current flowingthrough the light-emitting element becomes large, and the luminance ofthe light-emitting element is increased.

FIG. 20B is a specific circuit diagram of the pixel.

The pixel illustrated in FIG. 20B includes a transistor M1, a transistorM2, a transistor M3, a transistor M4, a transistor M5, a capacitor Cs, acapacitor Cw, and a light-emitting element 124.

One of a source and a drain of the transistor M1 is electricallyconnected to one electrode of the capacitor Cw. The other electrode ofthe capacitor Cw is electrically connected to one of a source and adrain of the transistor M4. The one of the source and the drain of thetransistor M4 is electrically connected to a gate of the transistor M2.The gate of the transistor M2 is electrically connected to one electrodeof the capacitor Cs. The other electrode of the capacitor Cs iselectrically connected to one of a source and a drain of the transistorM2. The one of the source and the drain of the transistor M2 iselectrically connected to one of a source and a drain of the transistorM5. The one of the source and the drain of the transistor M5 iselectrically connected to one of a source and a drain of the transistorM3. The other of the source and the drain of the transistor M5 iselectrically connected to one electrode of the light-emitting element124. The transistors illustrated in FIG. 20B each include a back gateelectrically connected to its gate; however, the connection of the backgate is not limited thereto. The transistor does not necessarily includethe back gate.

Here, a node to which the other electrode of the capacitor Cw, the oneof the source and the drain of the transistor M4, the gate of thetransistor M2, and the one electrode of the capacitor Cs are connectedis referred to as a node NM. A node to which the other of the source andthe drain of the transistor M5 and the one electrode of thelight-emitting element 124 are connected is referred to as a node NA.

A gate of the transistor M1 is electrically connected to a wiring G1. Agate of the transistor M3 is electrically connected to the wiring G1. Agate of the transistor M4 is electrically connected to a wiring G2. Agate of the transistor M5 is electrically connected to a wiring G3. Theother of the source and the drain of the transistor M1 is electricallyconnected to a wiring DATA. The other of the source and the drain of thetransistor M3 is electrically connected to a wiring V0. The other of thesource and the drain of the transistor M4 is electrically connected to awiring DATA_W.

The other of the source and the drain of the transistor M2 iselectrically connected to a power supply line 127 (at high potential).The other electrode of the light-emitting element 124 is electricallyconnected to a common wiring 129. Note that a given potential can besupplied to the common wiring 129.

The wirings G1, G2, and G3 can function as a signal line for controllingthe operation of the corresponding transistor. The wiring DATA canfunction as a signal line for supplying an image signal to the pixel.The wiring DATA_W can function as a signal line for writing data to amemory circuit MEM. The wiring DATA_W can function as a signal line forsupplying a correction signal to the pixel. The wiring V0 functions as amonitor line for obtaining the electrical characteristics of thetransistor M4. A specific potential is supplied from the wiring V0 tothe one electrode of the capacitor Cs through the transistor M3, wherebywriting of an image signal can be stable.

The memory circuit MEM is formed of the transistors M2, the transistorM4, and the capacitor Cw. The node NM is a storage node; when thetransistor M4 is turned on, a signal supplied to the wiring DATA W canbe written to the node NM. The use of a transistor with an extremely lowoff-state current as the transistor M4 allows the potential of the nodeNM to be retained for a long time.

As the transistor M4, a transistor containing a metal oxide in itschannel formation region (hereinafter referred to as an OS transistor)can be used, for example. Thus, the off-state current of the transistorM4 can be extremely low, and the potential of the node NM can beretained for a long time. In this case, an OS transistor is preferablyused as the other transistors included in the pixel. For the specificexample of the metal oxide, Embodiment 1 can be referred to.

An OS transistor exhibits ultralow off-state current characteristicsbecause of a large energy gap. Unlike in a transistor in which Si isincluded in the channel formation region (hereinafter referred to as aSi transistor), impact ionization, avalanche breakdown, short-channeleffects, and the like do not occur in an OS transistor; accordingly, ahighly reliable circuit can be configured.

Furthermore, a Si transistor may be used as the transistor M4. In thiscase, Si transistors are preferably used as the other transistorsincluded in the pixel.

Examples of the Si transistor include a transistor containing amorphoussilicon, a transistor containing crystalline silicon (typically,low-temperature polysilicon), and a transistor containing single crystalsilicon.

One pixel may include both an OS transistor and a Si transistor.

In the pixel, the signal written to the node NM is capacitively coupledto the image signal supplied from the wiring DATA, and the resultingdata can be output to the node NA. Note that the transistor M1 can havea function of selecting a pixel. The transistor M5 can function as aswitch that controls light emission of the light-emitting element 124.

For example, when the signal written to the node NM from the wiring DATAW is higher than the threshold voltage (V_(th)) of the transistor M2,the transistor M2 is turned on, and the light-emitting element 124 emitslight before the image signal is written. For this reason, it ispreferred that the transistor M5 be provided and that after thepotential of the node NM is fixed, the transistor M5 be turned on sothat the light-emitting element 124 emits light.

In other words, when an intended correction signal is stored in the nodeNM in advance, the correction signal can be added to the supplied imagesignal. Note that the correction signal is sometimes attenuated by acomponent on the transmission path; hence, the signal is preferablyproduced in consideration of the attenuation.

The details of the operation of the pixel in FIG. 20B are describedusing timing charts shown in FIGS. 21A and 21B. Note that although agiven positive or negative signal can be used as the correction signal(Vp) supplied to the wiring DATA_W, the case where a positive signal issupplied is described here. In the following description, “H” representshigh potential and “L” represents low potential.

First, the operation of writing the correction signal (Vp) to the nodeNM is described with reference to FIG. 21A. The operation may beperformed for every frame, and writing is performed at least once beforethe image signal is supplied. Furthermore, refresh operation isperformed as appropriate to rewrite the same correction signal to thenode NM.

At Time T1, the potential of the wiring G1 is set to “H”, the potentialof the wiring G2 is set to “L”, the potential of the wiring G3 is set to“L”, and the potential of the wiring DATA is set to “L”; thus, thetransistor M1 is turned on and the potential of the other electrode ofthe capacitor Cw becomes “L”.

This operation is reset operation for performing subsequent capacitivecoupling operation. Before Time T1, the light-emitting element 124 emitslight in the previous frame; however, the reset operation changes thepotential of the node NM, thereby changing the amount of current flowingthrough the light-emitting element 124. Thus, the transistor M5 ispreferably turned off to stop light emission of the light-emittingelement 124.

At Time T2, the potential of the wiring G1 is set to “H”, the potentialof the wiring G2 is set to “H”, the potential of the wiring G3 is set to“L”, and the potential of the wiring DATA is set to “L”; thus, thetransistor M4 is turned on, and the potential of the wiring DATA_W (thecorrection signal (Vp)) is written to the node NM.

At Time T3, the potential of the wiring G1 is set to “H”, the potentialof the wiring G2 is set to “L”, the potential of the wiring G3 is set to“L”, and the potential of the wiring DATA is set to “L”; thus, thetransistor M4 is turned off and the correction signal (Vp) is retainedin the node NM.

At Time T4, the potential of the wiring G1 is set to “L”, the potentialof the wiring G2 is set to “L”, the potential of the wiring G3 is set to“L”, and the potential of the wiring DATA is set to “L”; thus, thetransistor M1 is turned off and the operation of writing the correctionsignal (Vp) is finished.

Next, the operation of correcting the image signal (Vs) and operation ofmaking the light-emitting element 124 emit light are described withreference to FIG. 21B.

At Time T11, the potential of the wiring G1 is set to “H”, the potentialof the wiring G2 is set to “L”, the potential of the wiring G3 is set to“L”, and the potential of the wiring DATA_W is set to “L”; thus, thetransistor M1 is turned on and the potential of the wiring DATA is addedto the potential of the node NM by capacitive coupling through thecapacitor Cw. That is, the potential of the node NM becomes a potential(Vs+Vp) obtained by adding the correction signal (Vp) to the imagesignal (Vs).

At Time T12, the potential of the wiring G1 is set to “L”, the potentialof the wiring G2 is set to “L”, the potential of the wiring G3 is set to“L”, and the potential of the wiring DATA_W is set to “L”; thus, thetransistor M1 is turned off, and the potential of the node NM is fixedto Vs+Vp.

At Time T13, the potential of the wiring G1 is set to “L”, the potentialof the wiring G2 is set to “L”, the potential of the wiring G3 is set to“H”, and the potential of the wiring DATA_W is set to “L”; thus, thetransistor M5 is turned on, the potential of the node NA becomes Vs+Vp,and the light-emitting element 124 emits light. Strictly speaking, thepotential of the node NA is lower than Vs+Vp by the threshold voltage(V_(th)) of the transistor M2; here, Vth is adequately low andnegligible.

The operation of correcting the image signal (Vs) and the operation ofmaking the light-emitting element 124 emit light are described above.Note that the aforementioned operation of writing the correction signal(Vp) and the operation of inputting the image signal (Vs) may beconcurrently performed; however, it is preferable to perform theoperation of inputting the image signal (Vs) after the correction signal(Vp) is written to all pixels. In one embodiment of the presentinvention, since the same image signal can be supplied to a plurality ofpixels at the same time, the correction signal (Vp) is written to allthe pixels first, whereby the operating speed can be increased.

As described above, when the light-emitting element emits light with theuse of the image signal and the correction signal, the amount of currentflowing through the light-emitting element can be increased, and highluminance can be achieved. A voltage higher than or equal to the outputvoltage of a source driver can be applied to the gate voltage of thedriving transistor, so that the power consumption of the source drivercan be reduced.

This embodiment can be combined with any of the other embodiments andthe examples as appropriate.

Embodiment 3

In this embodiment, electronic devices of one embodiment of the presentinvention are described with reference to FIGS. 22A to 22D.

Electronic devices of this embodiment are each provided with a displaydevice of one embodiment of the present invention in a display portion.In the display device of one embodiment of the present invention, thenumber of display panels is increased, whereby the area of the displayregion can be increased unlimitedly. Thus, the display device of oneembodiment of the present invention can be favorably used for digitalsignage, a public information display (PID), or the like.

The display portion of the electronic device of this embodiment candisplay, for example, an image with a resolution of full highdefinition, 4K2K, 8K4K, 16K8K, or more. As the screen size of thedisplay portion, the diagonal size can be greater than or equal to 20inches, greater than or equal to 30 inches, greater than or equal to 50inches, greater than or equal to 60 inches, or greater than or equal to70 inches.

Examples of electronic devices include electronic devices havingrelatively large screens, such as a television device, a desktop orlaptop personal computer, a monitor of a computer, digital signage, anda large game machine (e.g., a pachinko machine); a digital camera; adigital video camera; a digital photo frame; a mobile phone; a portablegame console; a portable information terminal; an audio reproducingdevice; and the like.

The electronic device of this embodiment can be incorporated along acurved inside/outside wall surface of a house or a building or a curvedinterior/exterior surface of a car.

The electronic device of this embodiment may include an antenna. When asignal is received by the antenna, the electronic device can display animage, information, or the like on a display portion. When theelectronic device includes the antenna and a secondary battery, theantenna may be used for contactless power transmission.

The electronic device of this embodiment may include a sensor (a sensorhaving a function of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, electric current, voltage, electric power,radiation, flow rate, humidity, gradient, oscillation, odor, or infraredrays).

The electronic device of one embodiment of the present invention canhave a variety of functions such as a function of displaying a varietyof information (e.g., a still image, a moving image, and a text image)on the display portion, a touch panel function, a function of displayinga calendar, date, time, and the like, a function of executing a varietyof software (programs), a wireless communication function, and afunction of reading out a program or data stored in a recording medium.

FIG. 22A illustrates an example of a television device. In a televisiondevice 7100, a display portion 7000 is incorporated into a housing 7101.Here, the housing 7101 is supported by a stand 7103.

The display device of one embodiment of the present invention can beused in the display portion 7000.

The television device 7100 illustrated in FIG. 22A can be operated withan operation switch provided in the housing 7101 or a separate remotecontroller 7111. Furthermore, the display portion 7000 may include atouch sensor, and the television device 7100 may be operated by touchingthe display portion 7000 with a finger or the like. The remotecontroller 7111 may be provided with a display portion for displayingdata output from the remote controller 7111. With operation keys or atouch panel of the remote controller 7111, channels and volume can becontrolled and images displayed on the display portion 7000 can becontrolled.

Note that the television device 7100 is provided with a receiver, amodem, and the like. With use of the receiver, general televisionbroadcasting can be received. When the television device is connected toa communication network with or without wires via the modem, one-way(from a transmitter to a receiver) or two-way (between a transmitter anda receiver or between receivers) data communication can be performed.

FIG. 22B illustrates an example of a laptop personal computer. A laptoppersonal computer 7200 includes a housing 7211, a keyboard 7212, apointing device 7213, an external connection port 7214, and the like.The display portion 7000 is incorporated into the housing 7211.

The display device of one embodiment of the present invention can beused in the display portion 7000.

FIGS. 22C and 22D illustrate examples of digital signage.

Digital signage 7300 illustrated in FIG. 22C includes a housing 7301,the display portion 7000, a speaker 7303, and the like. The Digitalsignage 7300 can also include an LED lamp, operation keys (including apower switch or an operation switch), a connection terminal, a varietyof sensors, a microphone, and the like.

FIG. 22D illustrates digital signage 7400 mounted on a cylindricalpillar 7401. The digital signage 7400 includes the display portion 7000provided along a curved surface of the pillar 7401.

The display device of one embodiment of the present invention can beused in each of the display portions 7000 illustrated in FIGS. 22C and22D.

A larger area of the display portion 7000 can provide more informationat a time. In addition, the larger display portion 7000 attracts moreattention, so that the effectiveness of the advertisement can beincreased, for example.

It is preferable to use a touch panel in the display portion 7000because a device with such a structure does not just display a still ormoving image on the display portion 7000, but can be operated by usersintuitively. In the case where the display device of one embodiment ofthe present invention is used for providing information such as routeinformation or traffic information, usability can be enhanced byintuitive operation.

Furthermore, as illustrated in FIGS. 22C and 22D, it is preferable thatthe digital signage 7300 or the digital signage 7400 work with aninformation terminal 7311 or an information terminal 7411 such as auser's smartphone through wireless communication. For example,information of an advertisement displayed on the display portion 7000can be displayed on a screen of the information terminal 7311 or 7411.Moreover, by operation of the information terminal 7311 or 7411, adisplayed image on the display portion 7000 can be changed.

Furthermore, it is possible to make the digital signage 7300 or 7400execute a game with use of the screen of the information terminal 7311or 7411 as an operation means (controller). Thus, an unspecified numberof people can join in and enjoy the game concurrently.

This embodiment can be combined with any of the other embodiments andthe examples as appropriate.

Example 1

In this example, the results of considering the structure of anauxiliary wiring and actually fabricating a display panel are described.

[Auxiliary Wiring Example 1]

First, the pixel 130 a illustrated in FIG. 1A and the connection portion122 illustrated in FIG. 1B, which are described in Specific example 1 ofdisplay panel, were considered. In addition, a display panel wasactually fabricated on the basis of the results of the consideration,and the cross section of the connection portion 122 of the display panelwas observed.

When the connection portion 122 was devised under conditions where thepixel size is 225 square μm (13-inch high definition (HD)) and thedistance between the opening edge of the metal mask and the opening edgeof the pixel and the distance between the opening edge of the metal maskand the center of the connection portion 122 are each 20 μm, theaperture ratio of the pixel 130 a was estimated to be 41.1%. In the casewhere the common layers are formed in one step, the aperture ratio iscalculated to be 30%; thus, it is found that when the common layers areformed in two steps, the aperture ratio can be significantly increased.

Next, FIG. 23 shows a scanning transmission electron microscope (STEM)image of the connection portion 122 in the fabricated display panel. Asillustrated in FIG. 23 , in the connection portion 122, the commonelectrode 113 was connected to the auxiliary wiring 120.

[Auxiliary Wiring Example 2]

In addition, a method by which an auxiliary wiring and a commonelectrode are electrically connected to each other even when commonlayers which are shared by subpixels of a plurality of colors are formedin the entire display region of a display panel was considered.Furthermore, a display panel was actually fabricated, and whether theauxiliary wiring and the common electrode were electrically connected toeach other was examined. A specific method is described with referenceto FIGS. 24A to 24F.

First, as illustrated in FIG. 24A, a reflective electrode 125 a and atransparent electrode 125 b were formed in this order over theinsulating layer 101. Next, as illustrated in FIG. 24B, only thetransparent electrode 125 b was processed to form the pixel electrode111 b and the auxiliary wiring 120 b. Then, as illustrated in FIG. 24C,the reflective electrode 125 a was processed to form the pixel electrode111 a and the auxiliary wiring 120 a. At this time, the etching time wasadjusted so that the end portion of the auxiliary wiring 120 a ispositioned inward from the end portion of the auxiliary wiring 120 b,and thus the auxiliary wiring having an overhang shape was formed. Theprocessing was performed using wet etching, which allows isotropicetching. FIG. 25A shows a STEM image of an overhang-shaped auxiliarywiring which was actually fabricated. FIG. 25A shows that the auxiliarywiring having an overhang shape in which the end portion of theauxiliary wiring 120 a is positioned inward from the end portion of theauxiliary wiring 120 b was formed.

Then, the insulating layer 104 was formed (FIG. 24D). The insulatinglayer 104 was formed to cover the end portions of the pixel electrode111 a and the pixel electrode 111 b and not to cover the end portions ofthe auxiliary wiring 120 a and the auxiliary wiring 120 b. Then, asillustrated in FIG. 24E, the EL layer 112 was formed to be disconnectedby the overhang-shaped auxiliary wiring. Furthermore, as illustrated inFIG. 24E, the common electrode 113 was formed to be connected to theside surface of the auxiliary wiring 120 b. The results of measuring theresistance after the EL layer 112 and the common electrode 113 wereformed demonstrated that the auxiliary wiring was electrically connectedto the common electrode 113.

FIG. 25B shows a STEM image of an overhang-shaped auxiliary wiring whichwas actually fabricated. Note that the sample shown in FIG. 25B isdifferent from the sample shown in FIG. 25A. In FIG. 25B, the auxiliarywirings 120 a and 120 b are collectively referred to as the auxiliarywiring 120. As shown in FIG. 25B, the EL layer 112 was cut and theauxiliary wiring 120 and the common electrode 113 were connected to eachother.

[AUXILIARY WIRING EXAMPLE 3]

In addition, a structure in which an auxiliary wiring is provided on thecounter substrate side was considered, a display panel was actuallyfabricated, and the cross section of a connection portion between theauxiliary wiring and the common electrode was observed. A specificmethod is described with reference to FIGS. 26A and 26B.

As illustrated in FIG. 26A, a spacer 108 and an auxiliary wiring 106were formed on the counter substrate 121 side so as to be aligned withthe position where the insulating layer 104 on the insulating layer 101side was provided. In addition, a spacer 107 was formed over theinsulating layer 104. In other words, the spacer 107, the spacer 108,and the auxiliary wiring 106 were formed to be provided between twosubpixels. Then, the counter substrate 121 and the insulating layer 101were bonded to each other with a bonding layer 103 so that the auxiliarywiring 106 and the common electrode 113 were in contact with each other.

FIG. 26B is a top view of a display panel. The display panel includesthe pixel portion 71, the visible-light-transmitting region 72, and thevisible-light-blocking region 73 (lead wiring). The cross sections ofthree positions in the pixel portion 71 were observed. As shown in FIGS.27A to 27C, the auxiliary wiring 106 is in contact with the commonelectrode 113 in any of these positions.

Example 2

In this example, the results of fabricating the display device of oneembodiment of the present invention are described.

[Preservation Test of Display Panel]

A flexible display may be changed in shape because of the temperaturechange and the humidity change. In view of this, a preservation test wasperformed on a display panel 190, which is a flexible panel, bonded to asupport 195 as illustrated in FIGS. 28A and 28B.

Like the display panel DP in FIG. 12A, the display panel 190 includesthe visible-light-transmitting region 72 along two sides. At least partof the visible-light-transmitting region 72 overlaps with anotherdisplay panel, and thus does not overlap with the support 195.

As illustrated in FIG. 28A, in a comparative sample (Ref), the displaypanel 190 was attached to only the vicinity of the four sides of theouter edge of the support 195, whereby the display panel 190 was fixedto the support 195. As illustrated in FIG. 28B, in a sample (Sample),the display panel 190 was attached to the entire surface of the support195, whereby the display panel 190 was fixed to the support 195. For thesupport 195, an aluminum plate with a coefficient of thermal expansion(CTE) of 24 ppm/° C. was used.

In the preservation test, the sample and the comparative sample werepreserved at 30° C. for 12 hours, and then further preserved at 0° C.for 12 hours.

FIG. 28C shows the comparative sample (Ref) before the preservation testand FIG. 28D shows the sample (Sample) before the preservation test.FIG. 28E shows the comparative sample (Ref) after the preservation testand FIG. 28F shows the sample (Sample) after the preservation test.

As shown in FIG. 28E, the display surface of the comparative sample(Ref) after the preservation test has creases. In contrast, as shown inFIGS. 28D and 28F, no difference is observed in the sample (Sample)after the preservation test.

This indicates that when the display panel 190 is attached to the entiresurface of the support 195, a change in shape of the flexible displaycan be suppressed.

In addition, a preservation test similar to the above was performed onthe display panel bonded to the entire surface of the support with a CTEdifferent from that of the above sample. In the case where an acrylicplate with a CTE of 70 ppm/° C. was used, even when the display panel190 was attached to the entire surface of the support 195, the displaysurface had creases. In contrast, in the case where another resin plate,specifically, a glass fiber reinforced plastics (GFRP) plate with a CTEof 60 ppm/° C. was used, there were few creases in the display surface.

The above results show that when the flexible display is attached to theentire surface of the support with a low CTE, a change in shape of theflexible display can be further suppressed.

Furthermore, the flexible display might be changed in shape when a filmused for the flexible display absorbs water. The display panels 190illustrated in FIGS. 28A and 28B each include a portion that does notoverlap with the support 195, and the portion easily expands byabsorbing water and easily has creases as compared with other portions.This means that a film with a low water absorption rate is preferablyused.

[Method for Attaching Display Panel]

In the case where a plurality of display panels are arranged, analignment stage can be used to finely adjust the positions of theplurality of display panels. However, the alignment stage needs a space,which leads to an increase in size of a display device or an electronicdevice. Thus, a jig for attaching a display panel to a support with highaccuracy was formed so that the plurality of display panels can beplaced at desired positions without the alignment stage.

A method and a jig for attaching the display panel 190 to the support195 with high accuracy will be described with reference to FIGS. 29A to29D.

A jig shown in FIG. 29A includes a plurality of panel holders 416. Thejig includes adsorption pores in portions overlapping with the panelholders 416, and the display panel 190 can be vacuum-sucked when aswitch 417 is turned on. The panel holder 416 can hold down the displaypanel 190. With the use of the panel holder 416 in this manner, the side(the long side in this example) of the display panel 190 which does notoverlap with the support 195 can be fixed.

First, a separator film of a double-faced tape on the side attached tothe support 195 was separated, and the double-faced tape was attached tothe entire surface of the support 195. Note that a separator film on theside attached to the display panel was not separated and remained. Then,as shown in FIG. 29A, the support 195 to which the double-faced tape wasattached was placed at a predetermined position in the jig.

Next, as shown in FIG. 29B, the display panel 190 was placed over thesupport 195. The display panel 190 was provided on an adjuster 415 andplaced along a dotted line in FIG. 29B. Then, the switch 417 was turnedon, whereby the display panel 190 was sucked, and the display panel 190was held down by the panel holder 416.

Next, as shown in FIGS. 29C1 and 29C2, while the separator film wasseparated in the state where the display panel 190 was lifted, thedisplay panel 190 was attached to the support 195 little by little fromthe side where the display panel 190 was fixed (the panel holder 416side). Here, it is important to separate the separator film from theside where the display panel 190 is fixed by the panel holder 416, sothat the display panel 190 is bonded to the support 195 with highaccuracy.

FIG. 29D shows the state where the display panel 190 that has beenattached to the support 195 was removed from the jig. The deviationtoward the 0 direction was calculated to be approximately 0.02° or lessand the deviation was found to be small. With the use of the jig, thesupport 195 can be attached to the display panel 190 with high accuracy.Furthermore, FIG. 29E shows the state where the display panel 190attached to the support 195 displays an image. As shown in FIG. 29E, thedisplay panel 190 after being attached to the support 195 is found todisplay an image normally.

[Display Device]

Next, two kinds of display devices were fabricated using four (2×2) setsof a support and a display panel which were hardly changed in shape andattached to each other with high accuracy.

The first display device is a multidisplay in which a display panel anda driver circuit are modularized. FIG. 30 illustrates a side view of themultidisplay. FIG. 31A shows the display results and FIG. 31B is aphotograph of the side surface.

As illustrated in FIG. 30 , the display panel 190 is attached to onesurface of the support 195 (aluminum plate). The display panel 190 wasattached to the support 195 by using the method for attaching thedisplay panel described with reference to FIGS. 29A to 29E. The support195 has a curved surface whose curvature radius R is 5 mm, and thedisplay panel 190 is curved along the curved surface. The display panel190 has a portion extending from the support 195. The portion overlapswith an adjacent display panel 190. A driver circuit 372 is fixed on theother surface of the support 195. The display panel 190 is electricallyconnected to the driver circuit 372 with an FPC 374. Since the support195 and the display panel 190 are attached to each other with highaccuracy, the alignment stage does not need to be provided and aseamless image can be displayed only by fixing the display panel 190 toa designed frame. The sum of the thickness of the support 195 and thethickness of the display panel 190 (i.e., the thickness T in FIG. 30 )is 35 mm or less.

An optical member 240 includes a support member 292, a circularlypolarizing plate 295, and an anti-reflection member 296 in this orderfrom the display panel 190 side. For the support member 292, an acrylicplate was used. In the circularly polarizing plate 295, a linearpolarizing plate 295 a is positioned on the viewer side and aquarter-wave plate 295 b is positioned on the display panel 190 side.For the anti-reflection member 296, an anti-reflection film (alsoreferred to as an AR film) was used.

Furthermore, for example, a touch sensor is incorporated into thedisplay panel 190 or the optical member 240 or a touch panel is attachedto the display panel 190 or the optical member 240, whereby themultidisplay can have a function of a touch panel.

As shown in FIG. 31A, the fabricated multidisplay can naturally displaya nearly seamless image.

The second display device is a multidisplay in which a driver circuit isprovided apart from the display panel. First, the structures of threekinds of display panels are described with reference to FIG. 32 andFIGS. 33A to 33E.

FIG. 32 is a rear view of a multidisplay. In the multidisplayillustrated in FIG. 32 , one end of an FPC 374 s and one end of an FPC374 g are connected to each rear surface of display panels 190 a to 190d. Like the display panel 15B in FIGS. 17A and 17B, the conductive layeris exposed on the rear surface of the display panel, whereby an FPC canbe connected to the rear surface of the display panel.

Furthermore, the other end of the FPC 374 s is connected to one end of along FPC 374 a, the other end of the FPC 374 g is connected to one endof a long FPC 374 b, and the other end of the FPC 374 a and the otherend of the FPC 374 b are connected to a driver circuit (any of drivercircuits 372 a to 372 d). In this manner, power supply lines and signallines are led with the use of long FPCs, whereby only the FPCs areprovided on the rear surface side of the display panel, and a display inwhich the features of the thin and lightweight display panel areretained can be fabricated. For example, the display is suitable for awall-mounted display.

In addition, display panels having other structures are illustrated inFIGS. 33A to 33E. FIGS. 33A and 33C are bottom views of display panels,FIGS. 33B and 33D are top views of display panels, and FIG. 33E is aside view of a display device including the display panel illustrated inFIGS. 33C and 33D. As illustrated in FIGS. 33A and 33B, in the casewhere an FPC is connected to the display surface side of a display panel15C, the FPC may be bent to the rear surface side of the display panel15C. As illustrated in FIGS. 33C to 33E, an FPC may be connected to thedisplay surface side of a display panel 15D and the display panel 15Ditself may be bent on the rear surface side. The connection portion ofthe FPC and the connection portion of the IC in the display panel arepreferably bent on the rear surface side, in which case the non-displayregion of the display panel can be reduced and a display with a narrowbezel width can be obtained. As described above, even when the FPC isconnected to the display surface side of the display panel, the powersupply line and signal line are led with the use of the long FPC,whereby only the FPC is provided on the rear surface side of the displaypanel, and a display in which the features of the thin and lightweightdisplay panel are retained can be fabricated. Note that the angles atwhich the FPC and the display panel are bent are not limited to 180°.

Table 1 shows the specifications of the display panel. The pixelstructure of the display panel is the same as the structure of the pixel130 a illustrated in FIG. 1A, and the common layers of the EL layer areformed in two steps. The display panel includes an auxiliary wiringelectrically connected to the common electrode of the light-emittingelement. The structure of the auxiliary wiring 120 is similar to that inthe connection portion 122 illustrated in FIGS. 1A and 1B, and theauxiliary wiring 120 provided in the same layer as the pixel electrode111 is electrically connected to the common electrode 113. The displaypanel includes the pixel illustrated in FIG. 20B.

TABLE 1 Specifications Screen diagonal 13 inch Driving method Activematrix Resolution 1280 (H) × 720 (V) HD Pixel density 113 ppi Pixel size225 μm × 225 μm Aperture ratio 41.1% Source driver Chip on panel Scandriver Integrated

With the use of the four (2×2) display panels, a 26-inch WQHDmultidisplay was fabricated. The FPC was connected to the displaysurface side of the display panel. For the support of the display panel,a 1-mm-thick aluminum plate was used. The support has a curved surfacewith a curvature radius R of 3 mm. The display panel was bent along thecurved surface, so that the connection portion of the FPC and theconnection portion of the IC in the display panel were bent to the rearsurface side of the display panel as illustrated in FIGS. 33C to 33E.The display panel and the support were sandwiched between a pair ofacrylic plates. On the acrylic plate (the support member 292) on thedisplay surface side, the circularly polarizing plate 295 and the ARfilm (the anti-reflection member 296) were placed (see the opticalmember 240 in FIG. 33E). FIGS. 34A and 34C show the display results, andFIG. 34B is a photograph of the side. As shown in FIG. 34B, the totalthickness T of the support and the display panel (see FIG. 33E) isapproximately 13 mm, which is smaller than that of the firstmultidisplay (FIGS. 31A and 31B). As shown in FIGS. 34A and 34C, thefabricated multidisplay can naturally display a nearly seamless image.

Note that the measurement results of luminance of the above displaypanel when emitting light in an area which is 4% of the area of thedisplay region are shown. The measurement was performed through thecircularly polarizing plate. The luminance of display with only thedisplay data DATA in FIG. 20B was 918 cd/m², and the luminance ofdisplay in which the data DATA_W was added to the display data DATA was3149 cd/m². This indicates that when the data DATA_W is combined withthe display data DATA, high-luminance display can be achieved.

Example 3

In this example, the estimated results of aperture ratios of a pixel inthe display panel of one embodiment of the present invention and a pixelin the display panel of the comparative example will be described.

In this example, the pixel 130 a illustrated in FIG. 4A was used as thepixel in the display panel of one embodiment of the present invention,and the pixel 130 illustrated in FIG. 9A was used as the pixel in thedisplay panel of the comparative example.

In this example, the aperture ratio of the pixel was estimated under thefollowing conditions: the diagonal screen size was 13 inches, the numberof pixels was 1280 (H)×720 (V), the resolution was HD, and the pixelsize was 225 square μm. Furthermore, in this example, the apertureratios of the pixels in the case where the shortest distance (margin)between the metal mask and the subpixel was 10 μm, 15 μm, and 20 μm werecalculated.

FIG. 35 shows the estimated results of the aperture ratios of thepixels. In FIG. 35 , the horizontal axis represents the shortestdistance (margin) between the metal mask and the subpixel and thevertical axis represents the aperture ratio of the pixel. In the displaypanel of one embodiment of the present invention, the common layersincluded in the EL layer are formed in two steps; thus, “Two-stepmethod” in FIG. 35 corresponds to this panel. In contrast, in thedisplay panel of the comparative example, the common layers included inthe EL layer are formed in one step; thus, “One-step method” in FIG. 35corresponds to this panel.

The aperture ratio of the pixel in the display panel of the comparativeexample was estimated to be approximately 23% to approximately 52%. Incontrast, the aperture ratio of the pixel in the display panel of oneembodiment of the present invention was estimated to be approximately40% to approximately 65%. This indicates that the pixel in the displaypanel of one embodiment of the present invention is estimated to have ahigher aperture ratio than the pixel in the display panel of thecomparative example by approximately 15%.

The results in this example show that when the common layers included inthe EL layer are formed in two steps, the aperture ratio of the pixelcan be increased as compared with the case where the common layers areformed in one step.

Example 4

In this example, the results of manufacturing a display device includinga flexible display panel will be described. The display device in thisexample can be folded in two so that the display surface is placedinward.

FIG. 36A is a perspective view of the display device. The display deviceof this example includes a support 401 a, a support 401 b, a displaypanel 402, a support 403 a, a support 403 b, a gear 404 a, a gear 404 b,and a housing 405.

The support 401 a and the support 401 b are positioned on the rearsurface (the surface opposite to the display surface) side of thedisplay panel 402.

The display panel 402 includes a portion fixed to the support 401 a anda portion fixed to the support 401 b. For example, the display panel 402can be fixed to the support by using an adhesive (including adhesivetape and the like) or a suction film.

The display panel 402 includes an organic EL element as a light-emittingelement and a transistor including a metal oxide in a semiconductorlayer as a transistor for driving a light-emitting element. The displaypanel 402 is flexible.

The support 403 a and the support 403 b are positioned on the displaysurface side of the display panel 402 so as not to overlap with thedisplay region of the display panel 402 (so as to overlap with thenon-display region). The support 403 a is composed of three parts, andeach part is screwed on the support 401 a. Similarly, the support 403 bis composed of three parts, and each part is screwed on the support 401b. The structures of the supports 403 a and 403 b are not limited to thestructures illustrated in FIG. 36A, and can each be composed of one partor more.

The non-display region of the display panel 402 includes a regionbetween the support 401 a and the support 403 a and a region between thesupport 401 b and the support 403 b.

The housing 405 can store an FPC, an IC, a battery, and the like.

FIG. 36B shows the dismantled display device of this example. In FIG.36B, the support 403 a, the support 403 b, and the like are omitted.

The support 401 a is connected to the gear 404 a, and the support 401 bis connected to the gear 404 b. Since the gear 404 a and the gear 404 bare engaged with each other, the movements of the support 401 a and thesupport 401 b are synchronized, so that a change in shape of the displaydevice (a change in shape from the opened state to the folded state) isdetermined. Thus, the display panel 402 can be bent with a predeterminedradius of curvature. Since the display panel 402 can be prevented frombeing bent with a radius of curvature smaller than the predeterminedradius of curvature, the breakage of the display panel 402 due to anunintentional large power applied to the display panel 402 when thedisplay device is folded can be suppressed.

When the display device is opened, the support 401 a and the support 401b are in contact with each other. Thus, the entire display panel 402 canbe supported, and the impact strength and the scratch hardness of thedisplay panel 402 can be increased.

In the state where the display device is being opened or being folded,the support 401 a and the support 401 b are apart from each other; thus,a region which is not in contact with either the support 401 a or thesupport 401 b is generated in the display panel 402. The region is notsupported by the support 401 a and the support 401 b; thus, the impactstrength and the scratch hardness of the region is decreased in somecases.

To increase the impact strength and the scratch hardness of the displaypanel 402, an impact attenuating layer is preferably provided on one orboth surfaces of the display panel 402. Examples of the material for theimpact attenuating layer include silicone, urethane, and acrylic. Theimpact attenuating layer is preferably a rubber. The impact attenuatinglayer may be a gel. In this example, a display device in which asilicone sheet was provided on only the display surface of the displaypanel 402 and a display device in which a urethane sheet was provided onboth surfaces of the display panel 402 were fabricated.

FIGS. 37A to 37D are photographs of the display devices of this example.In the display device shown in FIGS. 37A and 37B, a urethane sheet witha thickness of approximately 0.22 mm is provided on both surfaces of thedisplay panel 402. In the display device shown in FIGS. 37C and 37D, asilicone sheet with a thickness of approximately 0.5 mm is provided onthe display surface of the display panel 402. Both of the displaydevices demonstrate favorable display and high durability.

REFERENCE NUMERALS

DP: display panel, 10A: display panel, 15A: display panel, 15B: displaypanel, 15C: display panel, 15D: display panel, 20A: light-emittingelement, 20B: light-emitting element, 21A: light-emitting element, 71:pixel portion, 71 a: pixel portion, 71 b: pixel portion, 71 c: pixelportion, 71 d: pixel portion, 72: region, 72 b: region, 72 c: region, 72d: region, 73: region, 74: FPC, 74 a: FPC, 78: driver circuit, 79:display region, 101: insulating layer, 102: light-transmitting layer,103: bonding layer, 104: insulating layer, 105: space, 106: auxiliarywiring, 107: spacer, 108: spacer, 109: protective layer, 110B:light-emitting element, 110G: light-emitting element, 110R:light-emitting element, 111: pixel electrode, 111 a: pixel electrode,111 b: pixel electrode, 112: EL layer, 112 a: EL layer, 112 b: EL layer,113: common electrode, 120: auxiliary wiring, 120 a: auxiliary wiring,120 b: auxiliary wiring, 121: counter substrate, 122: connectionportion, 124: light-emitting element, 125 a: reflective electrode, 125b: transparent electrode, 128: conductive layer, 128 a: conductivelayer, 128 b: conductive layer, 130: pixel, 130 a: pixel, 130 b: pixel,130 c: pixel, 130 d: pixel, 131: conductive film, 141: insulating layer,150: mask, 155: mask, 161: common layer, 161 a: common layer, 161 b:common layer, 163: light-emitting layer, 163A: light-emitting layer,163B: light-emitting layer, 163B_1: hole-transport layer for blue light,163B_2: blue light-emitting layer, 163G: light-emitting layer, 163G 1:hole-transport layer for green light, 163G 2: green light-emittinglayer, 163R: light-emitting layer, 163R_1: hole-transport layer for redlight, 163R_2: red light-emitting layer, 165: common layer, 165 a:common layer, 165 b: common layer, 170: region, 171: region, 172:region, 190: display panel, 190 a: display panel, 190 d: display panel,195: support, 201: conductive layer, 202: insulating layer, 203 a:conductive layer, 203 b: conductive layer, 204: semiconductor layer,208: insulating layer, 211: insulating layer, 212: insulating layer,213: insulating layer, 214 a: channel formation region, 214 b:low-resistance region, 214 c: LDD region, 220: transistor, 230:transistor, 240: optical member, 292: support member, 295: circularlypolarizing plate, 295 a: linear polarizing plate, 295 b: quarter-waveplate, 296: anti-reflection member, 301: transistor, 303: transistor,306: connection portion, 307: conductive layer, 308: conductive layer,309: conductive layer, 311: gate insulating layer, 312: insulatinglayer, 313: insulating layer, 314: insulating layer, 314 a: insulatinglayer, 314 b: insulating layer, 314 c: insulating layer, 315: insulatinglayer, 317: bonding layer, 318: bonding layer, 319: connector, 351:formation substrate, 353: separation layer, 353 a: separation layer, 353b: separation layer, 361: substrate, 363: bonding layer, 365: insulatinglayer, 367: insulating layer, 371: substrate, 372: driver circuit, 372a: driver circuit, 373: bonding layer, 374: FPC, 374 a: FPC, 374 b: FPC,374 g: FPC, 374 s: FPC, 375: protective layer, 401 a: support, 401 b:support, 402: display panel, 403 a: support, 403 b: support, 404 a:gear, 404 b: gear, 405: housing, 415: adjuster, 416: panel holder, 417:switch.

This application is based on Japanese Patent Application Serial No.2017-230849 filed with Japan Patent Office on Nov. 30, 2017, andJapanese Patent Application Serial No. 2018-095869 filed with JapanPatent Office on May 18, 2018, the entire contents of which are herebyincorporated by reference.

1. A display panel comprising: a first pixel electrode; a second pixelelectrode; a third pixel electrode; a first light-emitting layer; asecond light-emitting layer; a third light-emitting layer; a firstcommon layer; a second common layer; a common electrode; and anauxiliary wiring, wherein the first light-emitting layer is positionedover the first pixel electrode, wherein the second light-emitting layeris positioned over the second pixel electrode, wherein the thirdlight-emitting layer is positioned over the third pixel electrode,wherein the first light-emitting layer is configured to emit light of acolor different from a color of light emitted from the secondlight-emitting layer, wherein the first light-emitting layer isconfigured to emit light of a color identical to a color of lightemitted from the third light-emitting layer, wherein the first commonlayer is positioned over the first pixel electrode and the second pixelelectrode, wherein the first common layer comprises a portionoverlapping with the first light-emitting layer and a portionoverlapping with the second light-emitting layer, wherein the secondcommon layer is positioned over the third pixel electrode, wherein thesecond common layer comprises a portion overlapping with the thirdlight-emitting layer, and wherein the common electrode comprises aportion overlapping with the first pixel electrode with the first commonlayer and the first light-emitting layer between the common electrodeand the first pixel electrode, a portion overlapping with the secondpixel electrode with the first common layer and the secondlight-emitting layer between the common electrode and the second pixelelectrode, a portion overlapping with the third pixel electrode with thesecond common layer and the third light-emitting layer between thecommon electrode and the third pixel electrode, and a portion in contactwith a top surface of the auxiliary wiring.